Reproduce the problem and send me the debug.txt file that is generated in the %APPDATA%\PLSQL Developer 13 directory (e.g. C:\Users\\AppData\Roaming\PLSQL Developer 13).
The issue seems still exists in beta 6. I tried different scenarios (with plugins, without plugins). With the identical settings of program and oracle client: in ver. 12 is working correct, in ver. 13 - not...
Unfortunately, it still doesn't work. But behavior has changed.
Now the error message does not show, window opens, but does not any values in the "User" dropdown list...
We'll check it out. Can you go to the View Ribbon and check if the "Single Document" option is enabled? If it is enabled, can you check if it helps if you disable it?
Can you also let me know if you are using the 32 bit or 64 bit version?
"Single Document" option was enabled.
Bingo! After disable of "Single Document" option, issue was gone and "Compare User Objects" window now works as it should.
I was try it on both versions, behavior is the same.