I have had Media 100 get stuck on the “Media 100 is busy…” for quite a while as well. I just upgraded from Producer to Suite and it just started happening. Here is what seems to happen:
Start M100, open a program either new or existing.
Create a new title and click edit (also when editing an existing title)
Click “cancel” to get out of the title interface (without clicking “apply.”
Title interface goes away but M100 doesn’t seem to recognize that I’m back…thus still showing the “M100 is busy” alert.
Force quite M100.
Go back to create or edit a title….works normally.
Hope this helps a little.