Lightroom 3

Instead of uninstalling and reinstalling one should try to recreate the catalogue.  The full description is here:

<http://help.adobe.com/en_US/lightroom/using/WSBED0E080-63AF-4ba4-ACCF-EC48C4F92D6D.html#WS A0BE2627-F91E-4939-9D0B-FFCBF7672AC7>

Reinstalling any of the Adobe products will not solve anything because all the preferences and registry entries remain intact on a Windows system and I believe it is the same on a Mac system.  The surest way is to use Adobe Cleaner but this tool is so powerful that it removes all Adobe products and this is not recommended to anyone here.

I hope you will try recreating the catalog to see if it resolves itself.

Good Luck.

Prior to the error message, do you get a message along the lines of "Opening Catalog xxxxxxxxx.jpg.lrcat"?

If so, this is a common problem (fixed in LR4) which relates to a user error when trying to create a new catalog, and is best solved by resetting the preferences file. You can find instructions here:

http://www.lightroomforums.net/showthread.php?14226-Resetting-%28or-Trashing-%29-the-Light room-Preferences-file