I got the error "IOException: Unable to read resource content /tmp/xyz: Unable to move file."
My attachments folder permissions were correct but my temp folder was not. I had to correct the permissions on my temp folder to allow osTicket to move the files to the Attachments folder. For me my temp folder was C:\Windows\Temp
I searched the forums and Google and never came across this info so I wanted to share it for future searchers.