Imports has nothing to do with the problem. It's simply a developer shortcut so you don't have to type the full namespace when you use something in it. That's all, nothing more, nothing less.
What's at the heart of the issue is the reference itself and how it was created in the first place. What the copy local does is when you compile the app, it will go to the source where the file was originally found and copy it to the outputFolder of the app. For the most part, this should be turned on, UNLESS 1) the file you're referencing can be found on the target systems IN THE SAME PLACE. or 2) What you're referencing is found in the GAC, and can also be found in the GAC on the target system (see previous point about it being in the same place).
So... it sounds like you have a reference to thhis DLL, only it's not where the IDe is expecting it (app folder) ... and that's why you're getting the error.

-tg