I am not sure but the three items share a common file on a Mac it is called com.adobe.illustrator.plist and it resides in the same directory as the settings folder.
I do not know if it exist on Windows you cn remove it on the Mac and a fresh one is usually generated after relaunch of AI.
How this works on the PC I do not know but if it works the same way you can try trashing it and relaunching CS4 or CS 5 and see if the problem goes away.
Adobe has dropped support for Freehand import in CS6. You will have to either use an older version of AI and then save it to AI or open them in Freehand and then export to a format that AI can import.
open the Open file Dialog and see the files that illustrator CS6 can open. Here is the list of supported files that AI CS6 can open
I forgot to mention the point about CS4 and CS5 in my previous reply. Illustrator CS6 installs in a new folder hence it is not possible for it to affect CS5 or CS4. you may want to replair your CS5 install and that should work for you.
For repair you just ned to run CS instaler from the CS5 disk that youhave with you.
Adobe has dropped support for Freehand import in CS6.
Read the post again. Siegfried is having the problem with earlier versions after installing 6.
I do understand my first message was irelevant please read my second message
But that won't work either. He will need to uninstall both CS5 and CS6 and then reinstall both in order for it to work porperly.