It may also be a good idea to make sure that Communication Manager generated the error and not AE Services. It is very unlikely that AE Services generated an error like this but I think I have come across a case in the past where it did.
To check this, enable TSAPI tracing on AE Services. Then check the g3 trace file and make sure that AE Services sent the second Hold request, as an ASAI message, to Communication Manager and that Communication Manager responded with an error.
You can get instructions in the Devconnect Product FAQ "What is the procedure for enabling and accessing the AE Services logs for TSAPI (trace, tracing, g3trace, csta_trace)?". It is in the "FAQ: AE Services TSAPI -> General" section.