[Freeswitch-users] IVR not available with iLBC

i have configured FS to use iLBC for audio CODEC, it works perfect for any ordinary calls, but when making calls to IVR, the calls hangs up immediately after being established, the log on FS consloe is: [WARNING] mod_sofia.c:1279 Asynchronous PTIME not supported, changing our end from 20 to 30 [WARNING] switch_core_codec.c:704 Codec iLBC Exists but not at the desired implementation. 8000hz 30ms [ERR] sofia_glue.c:3062 Can't load codec? is it the problem that iLBC could not decode and play IVR sound files? so should i convert the .wav IVR sound files to iLBC format, or is there any better solutions since i may have to maintain two sets of sound files, one for iLBC and the other for other codecs as PCMU?