First thing I would do is check the drive for errors using the Disk Utility program, First Aid section. See if it find any errors on the drive.
Thanks for you suggestion, I gave it a go and issues were flagged.
Actually this whole issue has come since I moved my photos and catalog from computer to another. Everything seemed to be OK and this error is not on the source computer lightroom. As I am still setting up I have not made changes in the destination computer so I tried fix this by just copying again the lightroom files (ltcat, lrdata etc) from from the source to the destination computers but the above folder still remains. When I try to"Show Parent Folder" I get an "error code 19" message
Perhaps I should remove and reinstall lightroom. Do you think that would work?
Correction: It should read "... no issues were flagged"
If you still have all your image files and the LR catalog file on the original computer I would suggest Deleting everything off the destination (New) computer, including uninstalling LR and getting rid of all LR program files, then reinstall LR and copy over everything from the original again.
You should also check the permissions on your username folder to make sure your username has full Read & Write permissions.
One thing. Are you using the same exact User Name and password on both computers?
Thanks, I tried that too but it didn't work either. I got in touch with the Adobe support people and it turned out the catalog file was corrupted! To fix this problem we created an new catalog and imported from the old one. Fixed it! Did take some time though, about 1hr 45 for 18000+ photos. Not sure why we didn't use the back up catalog but they are the experts. Thanks for your help anyway, was a good learning experience, Regards Brendan