LR3: Catalog information lost

Hi,

I have XP and Win7 parallel on my PC. On both LR3 is installed which point to the same catalog file. All my raws are on one partition accessible by both OS.

Win7 was actually just a test installation because I made some benchmarks with Adobe Premiere.

Now comes:

I worked for while with the LR3 under Win7 and decided to deinstall it and continue working on my XP. After I did that and opened the LR in XP all my information were lost. I mean the .lrcat is still there but LR opens empty, no folders, no Flickr settings, nothing.

I must admit I haven't done a backup for a while (you can beat me for that), so work of 1 week would be lost.

Any ideas?