This looks like a permissions issue. Use apple-I to lookup the ownership and permissions on the drive. If its just a file dump set yourself as owner and copy the privileges to the enclosed files. This may take a while if there is lots on it. Don't do it if there is an OS on it! Or a backed home folder with your library folder in it. The rest of a home folder is OK.
You can sometimes tick an ignore ownership box for the drive from the info window. Tick it if it isn't ticked.
Also run repair permissions on all drives from disk utility.
These steps are listed in a stupid order. Check the tickbox first, the repair permissions, then change them manually.