Error getting file: -6: Not Supported

hey everyone.

I am suddenly unable to transfer files from my phone to my laptop.
I get the error message:
Error getting file: -6: Not Supported

sometimes the transfer will begin but then just stay at 0%

I have a htc m8. with android version 6.0 and htc sense version 7.0 (just did an update)
im using ubuntu 12.04

file transfers used to work fine until recently. The phone shows up and displays its contents. and it also transfers files to other computers no problem.
ive found a few writeups on fixes but nothing has worked for me yet.
any ideas would be greatly appreciated!
thanks in advance!