Problem SOLVED!
First thanks for your help Chris. I tried out your suggestions, but the first ones didn´t help:
"Update your ilok drivers:
www.ilok.com
Trash all pro tools prefs....
Go to Users > “your user name” > Library > Preferences....
-Delete 'com.digidesign.protoolsLE.plist', 'DAE Prefs' (folder), 'DigiSetup.OSX' and 'Pro Tools preferences'. "
Before reinstalling Pro Tools 9 - I took a last look at the Plugins Folder and mentioned, that all the plug-ins that didnt´t work were located in subfolders.
For backup-purposes I had copied all the plug-ins before. Through this process the system had asked me for my admin-password (I wondered about that). Well after backing up the plug-ins I didn´t have any subfolders in my backup-folder, just plain .dmp files - even from those plug-ins that had been in subfolders before.
The solution now was to delete the plugin-subfolders in the original plugins-folder and replace those plug-ins with the plain .dmp files from my backup-folder.
Everything´s running fine again
Thanks again!
Hannes