After executing sh /usr/local/freeswitch/skypopen/skype-clients-startup-dir/start_skype_clients.sh
I can see that the skype client process is absent
# ps -aux:
root      4353 0.0 0.3 126244 3092 ?        Ss   10:10   0:00 /usr/sbin/crond -n
pulse    30755 0.0 0.6 296340 6480 ?        S<l 10:54   0:00 /usr/bin/pulseaudio --system=true --daemonize=true --log-level=info --log-target=sys
root     30908 0.0 1.2 113140 12556 pts/0    S    11:01   0:00 /usr/bin/Xvfb :101 -ac -nolisten tcp -screen 0 640x480x8
root     30967 1.5 5.4 884616 55260 ?        S<l 11:11   0:19 freeswitch -nc
root     31041 0.0 0.0      0     0 ?        S    11:22   0:00 [kworker/0:0]
root     31048 0.0 0.0      0     0 ?        R    11:28   0:00 [kworker/0:2]
root     31054 0.0 0.3 151072 3964 pts/0    R+   11:33   0:00 ps -aux

I tried several times to kill process /usr/bin/Xvfb and start skype client again but failed.

I rebooted a system.

I deleted completely directories:
/tmp
/usr/local/freeswitch/skypopen/skype-clients-symlinks-dir

/usr/local/freeswitch/skypopen/skype-clients-configuration-dir
/usr/local/freeswitch/skypopen/skype-clients-startup-dir

and executed the "install.pl" script

cd /usr/src/freeswitch/src/mod/endpoints/mod_skypopen/install

./install.pl

However a skype client don't start.

Of course, mod_skypopen also failed:

2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1542         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1542 ][none           ][N/A,N/A] globals.dialplan=XML
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1539         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1539 ][none           ][N/A,N/A] globals.context=default
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1545         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1545 ][none           ][N/A,N/A] globals.destination=5000
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1548         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1548 ][none           ][N/A,N/A] globals.skype_user=xenia.obolenskya
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1551         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1551 ][none           ][N/A,N/A] globals.report_incoming_chatmessages=false
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1557         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1557 ][none           ][N/A,N/A] globals.write_silence_when_idle=false
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1560         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1560 ][none           ][N/A,N/A] globals.setsockopt=true
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1653         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1653 ][none           ][N/A,N/A] interface_id=1
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1664         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1664 ][none           ][N/A,N/A] name=skype101
2017-11-17 11:13:08.741603 [DEBUG] mod_skypopen.c:1670         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1670 ][none           ][N/A,N/A] Initialized XInitThreads!
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1693         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1693 ][skype101       ][IDLE,IDLE] CONFIGURING interface_id=1
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1730         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1730 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].name=skype101
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1733         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1733 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].context=default
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1736         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1736 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].dialplan=XML
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1739         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1739 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].destination=5000
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1742         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1742 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].X11_display=:101
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1745         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1745 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].skype_user=xenia.obolenskaya
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1748         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1748 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].report_incoming_chatmessages=0
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1751         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1751 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].silent_mode=0
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1754         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1754 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].write_silence_when_idle=0
2017-11-17 11:13:08.761605 [DEBUG] mod_skypopen.c:1757         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1757 ][skype101       ][IDLE,IDLE] interface_id=1 globals.SKYPOPEN_INTERFACES[interface_id].setsockopt=1
2017-11-17 11:13:08.761605 [WARNING] mod_skypopen.c:1759       [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [WARNINGA     1759 ][skype101       ][IDLE,IDLE] STARTING interface_id=1
2017-11-17 11:13:08.761605 [DEBUG] skypopen_protocol.c:1869    [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1869 ][skype101       ][IDLE,IDLE] X Display ':101' opened
2017-11-17 11:13:08.761605 [ERR] skypopen_protocol.c:1686     [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [ERRORA       1686 ][none           ][N/A,N/A] Received error code 5 from X Server

2017-11-17 11:13:08.761605 [ERR] skypopen_protocol.c:1687     [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [ERRORA       1687 ][none           ][N/A,N/A] Display error for 1, :101
2017-11-17 11:13:08.761605 [ERR] skypopen_protocol.c:1884     [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [ERRORA       1884 ][skype101       ][DEAD,IDLE] Fatal display error for :101 - successed to jump
2017-11-17 11:13:08.761605 [WARNING] skypopen_protocol.c:1910 [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [WARNINGA     1910 ][skype101       ][DEAD,IDLE] Removing skype interface #skype101
2017-11-17 11:13:08.841659 [DEBUG] mod_skypopen.c:1422         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1422 ][skype101       ][DEAD,IDLE] In skypopen_signaling_thread_func: started, p=0x7fa2cccb1d70
2017-11-17 11:13:08.841659 [DEBUG] mod_skypopen.c:1506         [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 1506 ][skype101       ][DEAD,IDLE] EXITING
2017-11-17 11:13:08.961605 [NOTICE] mod_skypopen.c:1788        [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [NOTICA       1788 ][skype101       ][DEAD,IDLE] WAITING roughly 10 seconds to find a running Skype client and connect to its SKYPE API for interface_id=1
2017-11-17 11:13:18.981616 [ERR] mod_skypopen.c:1801          [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [ERRORA       1801 ][skype101       ][DEAD,IDLE] Failed to connect to a SKYPE API for interface_id=1, no SKYPE client running, please (re)start Skype client. Skypopen exiting
2017-11-17 11:13:18.981616 [DEBUG] mod_skypopen.c:421          [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 421 ][skype101       ][DEAD,IDLE] interface 'skype101' STILL console
2017-11-17 11:13:18.981616 [DEBUG] mod_skypopen.c:431          [1.6.19+git~20171019T182535Z~f51b5d2dce~64bit ] [DEBUG_SKYPE 431 ][               ][IDLE,IDLE] interface 'skype101' deleted successfully
2017-11-17 11:13:19.961652 [CRIT] switch_loadable_module.c:1522 Error Loading module /usr/lib/freeswitch/mod/mod_skypopen.so
**Module load routine returned an error**