Have tested slavs as start up faction in amongst RTW units, and that works, so not the problem.

Will try Alemanni / roxolani in BI to make sure I can duplicate your result.

Quote (sorry haven't worked out how to do this in a box) "It works better by keeping the BI sharedpage_01.tga and replacing the factions' icons from BI with the RTW ones."

It was the BI sharepage.tga_01.tga we were using & replacing icons as suggested but that was what got us the Dacian problem. Is sort of liveable with as swimming units still work but Dacians in diplomacy/graph screens come up with swimming unit logo, it doesn't crash the game but is obviously not optimal!
Are you using the last icon, Bottom row, farthest right, in sharedpage_01.tga for any factions?