I made a fresh install with 3.5.6 (so no *.tdb, etc.). If I use XP (haven't tried other OS), open the server, go to file / printer properties / driver, the disabled 'add' button prevents me from uploading printer drivers. I also tested 3.5.4 and 3.5.5 - same issue.
Then I installed 3.3.14 and the 'add' button is enabled again and drivers can be uploaded.
I attach a screenshot and a level 10 debug log
Created attachment 6032 [details]
Level 10 debug log
Created attachment 6033 [details]
Screenshot of the Window with the disabled button
If I upload my drivers using 3.3.14, I can use them on 3.5.6, but the Buttons 'add', 'remove' and 'replace' stay disabled. Only 'properties' gets enabled.
The problem is gone in 3.5.8.