I recently noticed that if I haven't defragmented my hard drive, I get all sorts of file-related problems with games, including MXO, that have tons of files.
Try defragmenting your hard drive, then running the launcher again. If you still get errors, you may need to do a full systems check.
Take a look at Phi's rather handy guide to troubleshooting:
http://forums.station.sony.com/mxo/..._id=36300024020
And in particular, "How to Run a Full System Check":
http://forums.station.sony.com/mxo/..._id=12400011161
Post back here so we know if this does/doesn't resolve the problem.
Hope it helps! 