USB stick detected but can't be mounted
Solution 1:
The problem is most likely the partition table written by the manufacturer. Have a look at the answer on this question and see if it helps you.
Solution 2:
I have had exactly the same problem : a 8GB pendrive working like a charm or not mounting depending on the computer and on the usb port. I fund that this 8GB pendrive had a max current of 500 mA (5 times more than my other pendrives)! I am convinced it is the source of the problem.
Note : I fund the max power of the device with :
sudo lsusb -D /dev/bus/usb/xxx/yyy
where xxx and yyy are given by lsusb.
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Solution 3:
I had similar problem (with external HDD). I solved it in this way, that I inserted cable to other USB port. I supposed that tis one, which didn't work was USB3 and second was USB2.