In this case it looks like the download completed, and the Setup.exe was successfully launched, but some error occurred while terminating the running copy of PC Access.  Correct?
I am unable to duplicate this in house.  Can you tell me more about the systems.  Things like RAM, CPU, Clock rate etc. might be helpful in locating the problem.
FYI: At the point where the error is occurring your account files have been closed, they are actually closed before the download starts, so no data should be lost.  Still I don't want to have any errors so I would appreciate any information than can help me track this down.