Maybe this can help you, I found it on the Nortel site.
Delayed messages.
Event 55064 MWI message folder I/O error.
MWI does not light when user receives a message.
Event ID 38727 - Event from MWI[] : NBnot_ControlMWI:MWI Control failed Tapi_rc= -2147483576, Line= 0, DN=XXXX
Event 38750 - Event from MWI[] : ClientThread:Multiple MWI requests.Not executing. rc= 0, Request Action= 1, DN=xxxx
Cause:
MWI port in an unknown state.
Fix:
Reset MWI channel in the CallPilot and the associated Rolm PBX port.