Warning: translated frame write failed

Hi,
Since upgrading to 15.5 from 15.3 I am now seeing these warnings in the logs. Any advice on whats wrong?

[Aug 14 21:05:42] WARNING[11678][C-00001e79]: file.c:258 ast_writestream: Translated frame write failed
[Aug 14 21:05:42] WARNING[11678][C-00001e79]: file.c:258 ast_writestream: Translated frame write failed
[Aug 14 21:05:42] WARNING[11678][C-00001e79]: file.c:258 ast_writestream: Translated frame write failed

Added some fields to the log entries im getting in hopes of figuring out whats wrong:

[Aug 16 08:08:18] WARNING[29851][C-0000000a] file.c: Translated frame write failed (res = -1) (name = wav) (source = ulaw)
[Aug 16 08:08:19] WARNING[29851][C-0000000a] file.c: Translated frame write failed (res = -1) (name = wav) (source = ulaw)
[Aug 16 08:08:20] WARNING[29851][C-0000000a] file.c: Translated frame write failed (res = -1) (name = wav) (source = ulaw)
[Aug 16 08:20:34] WARNING[29851][C-0000000a] file.c: Translated frame write failed (res = -1) (name = wav) (source = ulaw)

All wav and ulaw stuff is loaded (my system wouldnt work without it).

codec_ulaw.so                  mu-Law Coder/Decoder                     19         Running              core
format_wav.so                  Microsoft WAV/WAV16 format (8kHz/16kHz S 1          Running              core
format_wav_gsm.so              Microsoft WAV format (Proprietary GSM)   0          Running              core