Had this happen sometimes with the DBW version of Pablo's MissionPro Combo, some people reported that if they click on the actual mission screen, it suddenly appears.
Check in the missions folder (under whichever nation you're flying) to see if DCG generated a directory for the campaign, and a mission file.
If so, then it's normally MissionPro, but you say there are no mods in JSGME? Never had this in a clean install, are you using stock campaigns or third party, was anything changed, as an error in the campaign files might cause the same thing. If DCG doesn't work in a clean install with no mods at all, and using the updated files, I can only assume there must be an installation error. Are you on Vista/Win7? Installed in Program Files?
I assume you're using 3.46, as this version supports IL2 4.101, previous versions do not, you probably know that, but didn't actually say which version.
You're right, it doesn't say that, I assumed DCG users here know where their stuff is as most of us have been using it for years and updating files through UP2, 410, HSFX4.1, now 501, and finally now DBW, however, as DCG actually belongs to Paul all the info is at his site, I assume you downloaded it from there, but since this isn't Paul's site you have a valid point, I'll add it to the post for any new users wanting to try it out.