@CJ_and_Darren Welcome to the Rockstor community,
From the following part of the Traceback:
It looks like something is still accessing this device. If it’s a drive that you had previously set up a share on and you have now stopped using it, i.e. experimenting a bit, then it could be that the original use hasn’t properly let it go. This might be related to your similarly timed post here:
If the program or mount that was previously using this device is properly removed / turn off then it may be that you need to do a reboot for it’s locks on that device to be properly cleared up.
Hope that helps.