That's a bummer.... I guess?

Words please, as none of us (we are volunteers, fellow software users)  have the codes memorized.

It all concerns W-2 inputs box 12a, in this case Code D...the critical Diagnostic reads,

"the letter code input for W-2 Box 12a is invalid. Please verify the information on the W-2 and correct the input. ref. #6071"

I've used Lacerte for over 20 years and entered a "million codes" and never have seen this!

Try deleting the D and reentering. Maybe a stray dot or something got in there. D is certainly a valid code.

Try Susan's suggestion; I tried it in a few client files and "d" works fine for me.  

Try it in a different client to see if it's working there; to eliminate a software wide problem.

And... let us know. These oddities worry me.