ATB80003I APPC data structures for the TP are in use by another process.

Detecting Module:

Explanation
 A TP called an APPC/MVS TP conversation service.
The system could not process the request because APPC/MVS data structures
for the TP are in use by another process.
 One of the following
situations could cause this error:  The TP called the TP conversation service while the system was
processing a call to another conversation callable service for the
same conversation. For example, the previous call could have specified
a Notify_type of Notify_ecb, and the TP could have called the second
service before the system could post the ECB (to indicate the end
of asynchronous processing for the previous call).
An internal error occurred in APPC/MVS.

System action
 The system returns a product_specific_error (decimal
20) return code to the caller of the conversation service.

System programmer response
 Contact the IBM Support Center.

Programmer response
 Ensure that processing for a previous call
to an APPC/MVS service is complete before you call another APPC/MVS
service. If a Notify_type of Notify_ecb was specified on the previous
call, wait on the ECB before calling the next service.  If the problem
persists, contact the system programmer.

Source
 APPC/MVS

Detecting Module:

ATBVSRB