Unbelievable.  I posted my same frustration earlier today on the ProSeries Support Group on Facebook.  Here's one response I got from another user:

"Here is what I did. Go to 1116 Comp worksheet enter the carryover amount in disallowed column, error goes away. Lose the carryover for current year but maybe can be re-entered in a later year and hopefully form can be e-filed then. No way I am waiting until 3-31 to file a return by mail for a small carryover. Just my 2 cents."

I'll have to think about the risk that the IRS won't like me re-entering it in a later year.

BTW, I just found on the IRS website that the PDF of Schedule B was issued last December. So why isn't it available for efiling?