Did you migrate your copy of InDesign to a new computer using the Migrate feature? If so, that doesn't work. You would have to use the Adobe Cleaner utility to clean out all your CS stuff, then reinstall from the original media or download file.
Thanks for the useful answer Steve. I indeed used the Migrate feature to install my software on a new MacPro and everything (the Adobe CS5.5 applications included) seems to work fine exept Indesign. I alreade have tried to find a new install-file of the CS5.5 Design Premium but I couldn't find anything like that. I bought it online without a hardware copy. Any suggestions?