The following procedure should get you up and running again without having to re-catalog your images:
1) Open the Catalog Management window (Catalog->Catalog Management) look in the Local Catalogs section and find your catalog.
2) Expand the options by clicking on the triangle that appears before the name of your catalog and click the Forget button.
4) Click the "Locate Existing Catalog..." button. Use the filesystem dialog to find your catalog (you just need to choose the folder.)
5) Expand your catalog, then expand the Maintenance section and click the "Reintegrate Forgotten Catalog".
When it finishes, your catalog should again be functional.
HTH,
-Kirk