Hi - I have the same problem ...
Just installed the default ("perfect setup") ispconfig installation with no problems, all looks fine. I did not have changed any settings, except to add a reseller and a client account (reseller added as admin, client added as reseller)
The only difference from the default setup I made was the mysql databasename/prefix: I used ISPCONFIG (default was "ispconfigdb" I think)
the result after adding a web in "site management" is
"You cannot assign MySQL databases to this website."
"Sie können diesem Web keine MySQL-Datenbanken zuordnen." (same in german)
This occurs as admin and as reseller and with a web-template or with "individual settings", or with "-1" allowed databases or with a number, eg. 10
So its not possible to create a new web with databases (one or more)
I switched from admin to reseller and backward by logging out and closing the browser. So all session-data should have been deleted.
Does anybody have a hint for me? Many thanks in advance!
And - last but not least - with my first posting I want to thank for providing ISPConfig! Not only ISPcofig for itself must be great (I could not try it until now :-), even the documentation, installation at last this support forum and the community is outstanding of many projects I know!