I’m frustrated

Lightroom 4 does not import a correct LR3 catalog.

Every time I try to import a LR3 catalog (I veryfied and optimized this catalog with LR3 before) with Lightroom 4 on my MacBook Pro (10.7.3) I get this error message:

"Ein interner Fehler ist aufgetreten. Database "/Users/bm/Pictures/Lightroom/Lightroom 4 Catalog.lrcat": columns LC_idx_filename, folder ara not unique Statement: UPDATE AgLibraryFile SET folder = ? WHERE id_local = ?;

and the catalog is not importet.

What is going wrong here?
What can I do?

With best regards
2 people have
this problem