With newly installed system (Running FreePBX Version: 1.810.210.57-1) with just one SIP trunk setup occasionally calls are dropped and I get the following error:
[2012-03-21 15:21:19] NOTICE[20291]: pbx.c:4270 pbx_extension_helper: Cannot find extension context ''
[2012-03-21 15:21:19] WARNING[20291]: pbx.c:10588 pbx_parseable_goto: Priority '' must be a number > 0, or valid label
== Spawn extension (from-trunk, fax, 1) exited non-zero on 'SIP/link2voip-sw1-000000fe'
-- Executing [h@from-trunk:1] Macro("SIP/link2voip-sw1-000000fe", "hangupcall,") in new stack
-- Executing [s@macro-hangupcall:1] GotoIf("SIP/link2voip-sw1-000000fe", "1?theend") in new stack
-- Goto (macro-hangupcall,s,3)