Have been sing backup fine for some time.

But on last attempt to ope the applicatiion, I get a dialogue error box -

Eror in catalog which needs to be repaired.

I select "Yes", and the app closes. After some time, I try to reopen, but get the same error - it deos not seem to repair,even though I have selected "Yes".

Any ideas how to solve please??

Regards

Best advice I can give you is to delete the catalog directory. It will rebuild the directory, although you will lose all the listings in it. Even without it, you can do restores. Just use device view on the restore and point to the backup file or media. It will build a temporary catalog to allow you to pick what you want to restore.
Other things you may try is do a compress of the catalog.
Questions for you on the maintenance of the catalog. Do you delete old entries in the catalog when you delete the old backup files? I have never had the catalog problem, although others have, but it may be due to the maintenance I do when I clean up old backups.