My historical league problems with illegal roster numbers is happening because the draft isn't automatically coming up. I have it all setup to run as normal, but no one is actually being imported from Lahman.
I've tested it in 3 different dummy leagues now, only the first draft goes through, then nothing, causing each team to have no reserve left after a few years.
It's been going on a bit in this thread since yesterday:
Leagues no longer import historical rookies