Unmount SSD drive do not work

WD SSD Products WD SSD Drives & Software
1

Hi all,
When I try to unmount my SSD sanDisk pro 1 TB it tells me:
it is stil working in the background, Close the program and try again .
But there is no program running. What to do?
I made refresh few times, but it did not work.
Thanks for your help
Racin