Some readers are just incompatable. I had a similar problem with a Sandisk memory stick and one of my readers, but it worked fine in other devices and readers. Same goes for SD style cards, as well. I have a few that when I try and access them, they say "Disk not formatted" but then it works fine elsewhere.
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Urban De-Development
* Athlon X2 4200 | 2048M RAM | 160G HD | 7600GT
* C2D T5250 | 2048M RAM | 160G HD | Intel x3100
* G4 1.33GHz | 512M RAM | 40G HD | Radeon 9200
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