Okay, here's what I suspect.

I just saw your thread in the JCS forum, asking for JCS. And I think I know what is going on here.

I think you have most likely illegaly downloaded the OEM version of the game from a well-known abandonware site and now are trying to run levels created with JCS on it. The level format used in the OEM version is not compatible with the level format used in the final version, which is why you can't use JCS. This is also why you had to download the official tilesets somewhere.

Does the version number in the main menu of JJ2 (left-bottom corner) say something like 1.00g?