Wild guess, is this the download u-boat missions from Amazon? That's what I bought, and my experience was that it worked like the US congress. The actual installation wouldn't work at all, I had to use the Amazon downloader, which then proceeded to read the location of the original install from the system registry with no option to redirect it to another folder. When I had to do a system restore to fix another problem the 1.5 version would no longer work - it's looking for registry keys that no longer exist, so I got an error message whenever I tried to launch 1.5.
http://www.subsim.com/radioroom/showthread.php?t=231318
I might try to reinstall it at some point in the future, but for now I just gave up and went back to the 1.4 version. That one was originally a download from Direct2Drive, which had no DRM minefields.