I would check the compression first with

# uncompress /opt/globusback2/needed_backups/apglsg.tar.Z


If that returns a zero return code, then the compression, at least, is fine, but the tar archive itself is corrupted. In that case, depending on where the corruption is in the archive, you still may be able to extract some of the files. Try a directory listing on it:

# tar tvf /opt/globusback2/needed_backups/apglsg.tar

Good Luck!