Im getting the same error

For what it's worth, I've gotten this error from day one. I installed to a drive different than C and am launching the x64 executable.

It's annoying, but doesn't seem to have any impact on anything. My window pops up twice, I can click cancel or continue - and either way the game starts right up.

Would love to have it fixed, though....

You know what's good about an error that can be applicable to other games? Well, I did a search for this problem and apparently it was a problem for Windows 7 users on a forum for a game called Maple Story. What they figured out, and I have no clue as to how, is that there are "fake drives" that Windows 7 has that are essentially USB devices, listed as Generic. The game looks at these generic drives when it does its check for the Disk drive, which you should have at least one real drive. When it detects these generic drives, it reads them as missing.

Go to the Computer Management (Local) window by right-clicking My Computer (or just Computer in the start menu) and select Manage. Under Device Manager in System Tools on the left panel, you can expand the Disk drives icon to see the Generic - devices that are mostly USB. There is one drive that should be your true drive. Only disable the drives named "Generic" by right-clicking them and selecting disable. This should eliminate the pop-up window that the game creates.