An invalid character was found in text content.

I'm trying to bring feature data within a geodatabase into an .mxd document (ArcView 10.0). When I attempt to add it I get the "Open Failed" message: Error opening feature class. An invalid character was found in text content.

I've noticed this has happened to a couple of feature files within a geodatabase that were used in .mxd's prior to compression. Now the data is compressed in the geodatabase. I tried to uncompress to see if they'd work but still do not. Any suggestions?

Thanks!