The problem suddenly corrected itself after a few hours, so I assumed it was some sort of cache problem.
(although I had previously updated cache under prefs & my browsers cache with no luck). But it seems ok now.
Herko Coomans wrote:
the problems with modules comes from the fact that when you change mainfile.php, you have to 'update' every module in the system admin -> modules page. This will propagate the changes in mainfile.php everywhere.
Herko