The federal boxes at the top of screen 1 are not checked.

In Settings, the "default to efile" box is set to "no". The IRS does not accept e-file for Form 5227.

On screen 47, I suppressed Form 1041-A.

Why am I receiving critical diagnostic 14166?

It says:

"e-file:  The federal return was selected for e-file, but Form 1041 is not applicable for this file.  Turn off federal for e-file by unchecking the box in Client Information. (ref. #14166)"

This causes a validation error, apparently, that will prevent e-filing of the state (PA) return.