Finder always prevents simple external hard drive eject

I regularly connect external hard drives to my MacBook Pro and recently I cannot do a simple eject either through disc utilities, or finder, or any other way, keep getting error message to stop finder action and try eject again. The discs I use are for time machine back-ups and I use them to access backed up files.

I have to force quit finder every time and am concerned that this will eventually corrupt the data and/or the back up disc. Any suggestions?