I also got this code, but in my scenario the called party didn't generating fax tone. I have tested FreeSWITCH with Images as well but never got such kind of code in that case.

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From: "Steve Underwood" <steveu@coppice.org>
To: "FreeSWITCH Users Help" <freeswitch-users@lists.freeswitch.org>
Sent: Wednesday, July 18, 2012 5:00:14 PM
Subject: Re: [Freeswitch-users] Fax processing not successful - result (48)        Disconnected after permitted retries

On 07/18/2012 06:54 PM, afshin afzali wrote:
> Hi,
>
> There are some inbound fax sessions which I got error code 48 (and in
> some cases 49).
>
> FreeSWITCH Version 1.0.head (git-54ddef0 2011-12-06 21-53-45 -0600)
> AS5350XM Voic e / Fax ( T.38 ) Gateway
>
> I've noticed that this error appears in cases which there are complex
> documents (graphics or gray areas).
> appreciate all comments !
If you have graphics, the pages generally take a lot longer to send. It
is not uncommon for T.38 gateways to have stupidly short timeouts, which
will cause a call to drop after a page has been in progress for just one
minute, or one and a half minutes. Could that be your problem?

Steve