Subs with marines

Hello! I am trying to carry marines with my subs, and it dosent work in any game. It has been a long time since last time I playd, but then I had all the upgrades and it worked. I get the error: "This transport unit can onley carry [unidentified unit] 3. How comewhen I have choosen marines? And tried with the others also.? I searched the forums, but did not find a post on this problem.
Ty for answers

Kvracing

It was default map I guess. Tried both in Europe and the whole world map.

If it was on a default map, then it is a bug. If it was on a scenario/map created by a fellow player it could've been that map/scenario creator defined subs as non-transport. In any case it is weird. Just happened to me in one of the early WWII versions; appearing an error.

It was obviously the map, I played europe now and it worked.