Finder not finding files on external hard drive

Recently the finder application stopped finding certain types of files on an external drive. The external drive (WD 80GB) is recognised and I have access to all files, however, when I search for specific files in the finder window it wont find pdf, txt, doc files. It does find picture files such as jpg. I have tried using the drive on my laptop (snow leopard) and macmini (leopard) and have the same problem.

Thanks for any advice

I have checked the preferences and its not on the privacy list.

The finder does find some files on the drive. I thought it was only image files but it appears to be finding all files except those in one folder. Everything appears to be normal under the settings for that folder (ie. its not locked).

Thanks