We dont' use Flexi, but have had this problem in Onyx. When the file gets hung up and won't go away this is what we do for ONYX (not sure if Flexi is similar)
Go to the C drive / Programs / ONYX - open the ONYX Program files, and scroll down until you find a file that is named "Work". Open the work file, and you will see your file, probably by date, and it will say it is on hold or whatever indicator it gives you in the cue. Delete that file. Problem solved. That's in ONYX. I would imagine that Flexi has something similar?