I use Custom letters (edit the Standard) but I've been using the without a problem this year.

Theyre included.  Im not sure why anything is greyed out for you, but make sure yovue got the boxes checked your Print Options > Control Which Letters Print

Did you ever resolve this as my C Corporation letters disappeared after I had done an edit on the Standard letter. Poof!

I can't figure out how to bring them back.

Changed to another return type and back and the letters were back.

I have had that problem occassionally, as well as when trying to print an individual form It is also grayed out.  I go to the state return and then back again and it starts working for a while.

If you happen to be in a state file the letters won't access unless you are in the Federal return.

You flip to the state and back to the federal that should solve the gray box problem.

My letter tab is grayed out after I print a copy. So I go into the state and back to federal and it's no longer grayed out.