Possible corrupt USB drive?

I have Unraid 6.1 virtualized in ESXi 5.5 with the Plop method. It's been running this way since Unraidv5, and I've experienced this issue off and on, but it has become more frequent recently. The issue is this: after a seemingly random period of time, my flash drive becomes "corrupted" (I'm using quotes because I don't know what else to call it). I lose the ability to navigate to \\tower (I can hit it by IP but not by DNS name). The web GUI still works with http://tower, though. I have a folder on the root of the flash drive called "custom" that houses some scripts to copy data and the like. Once the drive becomes "corrupted" i can no longer navigate to anything but the stock folders on the flash drive. It's as if the custom folder doesn't exist: ls -l doesn't show anything, and if I try to cd /boot/custom, it just doesn't work; pressing Tab to autocomplete the path doesn't work either).

To fix this, I have to power down Unraid, but as soon as I stop the array, the page refreshes and shows me the "tools" tab and tells me that there is an error reading the flash GUID and to contact support (which I did, and Tom suggested I post here). I then change back to the Main tab, and Unraid tells me I have too many disks and need to upgrade my license. I then power off Unraid and insert the Unraid USB key into my PC, at which point Windows tells me that there's a problem with this drive and it needs scanned. I always choose Scan & Fix, and it completes, but never finds any errors. I've tried formatting the drive and installing Unraid from scratch many times (backing up the Config folder) but the issue still exists.

Any help would be greatly appreciated. I've attached a screenshot of the flash GUID error page, and my most recent syslog can be downloaded from here: https://www.dropbox.com/s/rufgmjnh5hbfcbl/syslog_2015-08-31_21.39.02.txt?dl=0

Edit: I also have noticed that once all this starts happening, ESXi no longer sees the flash drive, either.

I've never had a problem with my flash disk and I don't virtualise Unraid, but FWIW each time I put the flash disk in a Windows machine it always tells me it's corrupt and needs scanning, the scan takes about five seconds and no errors are found.

May not be terribly useful in solving your issue but I thought it might be helpful to know.

Went through the process to fix my flash drive just after I posted this, and already it's jacked up again. It seems to have ran a parity check last night, but here's what it returned:

Last checked on Thu 03 Sep 2015 07:04:44 PM CDT (today), finding 0 errors.

Duration: Warning: Division by zero in /usr/local/emhttp/plugins/dynamix/include/Helpers.php on line 98 . Average speed: 0.0 B/sec

I'm thinking the flash drive is going bad, does anyone have any flash drive checking utilities they would recommend?