Flash Drive No Longer Recognized

Question

I purchased a new PNY Turbo 3.0 128 GB Flash Drive, formatted it as Mac OSX Journaled, transferred files to it, encrypted it, used it for about 30 minutes on my iMac, then it disappeared while navigating in Finder.
The flash drive does not show in Finder, Disk Utilities, or System Information.  Yes, show external drives is checked in Finder Preferences.
The USB is recognized in an older Macbook using a much older OS, although I can't view the contents and a message on the Macbook says that I need to put the drive into a device with an updated Mac OS.
No other user accounts on my iMac can view the flash drive.
So far I have done numerous restarts, shutdowns, and remounts, reinstalled Mavericks (again), repaired disk permissions, etc. 
This is the second issue I've had with an Apple formatted and encryped flash drive disappearing.  I've put an entire Sunday afternoon reading through threads and troublshooting this, and looks like some people just accept it as another thing that doesn't work on their Mac or go try different brands of flash drives until one works.
Suggestions or recommendations anyone?  I would like to keep this flash drive (it does have the Mac symbol on the packaging) if possible.

Answer 1

Did you ever get a satisfactory response to this?
I too have just encountered this issue.  I have a PNY USB 3.0 128MB flash drive.  I used it successfully for several months.
Today, connecting it to a brand new Mac Mini, 10.10, it is not recognized.  It's not just that it isn't recognized... It's not even showing up in Disk Utility.  The only indication I have that the system has detected it is this log message:
2014-10-26 12:20:55.000 PM kernel[0]: USBMSC Identifier (non-unique): 09031000003796153712 0x154b 0xfa05 0x1075, 2
Also, it shows up in System Information, in the USB Device Tree, but nowhere else.
I then tried it in my Retina MB Pro (2.3GHz i7) running 10.9.5, where I had always successfully used it, with the exact same results.
It appears that the OS is failing to load the driver, or perhaps something in the USB negotiation is failing.
I tried it on a couple of Macs, running 10.9.5, both USB2.0 and USB3.0, with no luck.  My old Snow Leopard 2005 iMac recognized it, but the filesystem was too new for it to read it. (It is an encrypted USB volume).  I was, however, able to copy the raw disk image, even though that mac couldn't read it.  I am hoping to access the files that way.
Now... I just put the USB Key into another of my Macbook Pros, an old 2.33GHz Core2Duo running 10.7.5, and this machine was able to access the encrypted partition with no problems at all.
So, I conclude that this is some problem related to 10.9.x, since both USB2.0 and USB3.0 Mac's running 10.9 were unable to recognize the disk, yet a 10.7.5 machine with USB2.0 reads this disk fine.
I'm hoping to get a suggestion from someone on how to best go about finding the root cause of this issue...
Thanks,
Pat