Sounds like your USB Stick is Corrupt? Had this problem with my Aero, in the end had to replace my USB stick completely, tried formatting my stick back to default, even tried re-formatting it with a program off the internet (FAT32), to no avail, I went out and bought a Sandisk Cruzer edge 64 GB, had no problems since, one word of advice is that, most of the new memory sticks come with Security built in, I would not recommend setting up a security gateway, as this will cause problems when you try and establish a wireless link with your I.O.S / Android device, hope this helps,
Adrian.