The CICS MSGUSR shows an attempt to purge the Intertest CICS ISER long running task that is required for InterTest for CICS to properly function in CICS.
In the most recent MSGUSR file that you sent in it shows an attempt to purge the ISER long running task that is required for InterTest for CICS. In fact, it shows two attempts to purge this task.
DFHAP1900 DATE TIME TCICSRJE NONE TSEQ ISER SET TASK(36420) PURGETYPE(FORCEPURGE) RESP(NORMAL) RESP2(0).
Despite the purge, the ISER task continues to run and another ISER task is started up and this can cause the posting of the duplicate wait on an ECB.
The ISER task is started when InterTest starts up from the PLT (or the CNTL=START command) and must continue to run for Intertest CICS to function properly. So the task should not be purged. If the purge request is a
result of a "purge of long running tasks", by OMEGAMON for example, then this task should be excluded from the list.
If it is necessary for some reason to stop this task from executing, the best way to do that would be to terminate InterTest and restart it using the CNTL=END and CNTL=START requests.