After upgrade to 9212 from an old version long long ago (as the correct path and steps told by ManageEngine website), we found that all technicians are unable to merge requests.  We always get below error message in a yellow box on the top of the page when click merge:

FAILURE :Problem while trying to merge this threaded request with the selected request. Please report the problem to the system administrator. Support file will have the error trace to analyze the problem and which can be created at Support -> Create Support File.

Except this, seems everything works fine in the new version. 

Please help........Thank you very much!