Error processing via header

I want to know when this error occurs

[Aug 27 18:49:36] WARNING[32192] chan_sip.c: error processing via header, will send response to originating address [Aug 27 18:49:36] NOTICE[32192] chan_sip.c: No header field 'Via' present to copy [Aug 27 18:49:36] NOTICE[32192] chan_sip.c: No field 'From' present to copy [Aug 27 18:49:36] NOTICE[32192] chan_sip.c: No field 'Call-ID' present to copy [Aug 27 18:49:36] NOTICE[32192] chan_sip.c: No field 'CSeq' present to copy [Aug 27 18:49:36] ERROR[32192] sip/reqresp_parser.c: received request without a Via header [Aug 27 18:49:36] ERROR[32192] chan_sip.c: error processing via header

When the SIP request is badly damaged - my guess it has been truncated. You would need to enable sip debugging to see exactly why.