After installing C4 Complete and adding the Wild Mana mod under win10, BtS started and worked fine once. Now, when starting BtS, Warlords loads instead. C4 and Colonization will also start (and run), but BtS simply won't. Re-installation didn't fix the issue. I appreciate any helpful advice.

I'm not familiar with the Wild Mana mod, but since you have installed a mod and the game doesn't run, that would be the main suspect. Try to remove the mod and see if BtS will run, or alternatively re-install the game without the mod. Could be the mod is causing some problems for BtS, or is installed incorrectly (don't know, as I haven't heard about that mod).

That's what I did (both measures). Unfortunately, even if the loading screen shows BtS, Warlord runs. Nevertheless, thanks for your suggestion.