Is it the Payer ID withholding entry that asks for a 14-character entry that ends with WTH?
If so, first of all be sure there are no hyphens (dashes) and no spaces.
I have seen a couple of users say it worked when they used lower case for the ending "wth" instead of capital letters. I realize that's quirky and anecdotal, but they say it worked for them. Please report back your results.