W-2 box 12 has nothing to do with itemized deductions or property tax. What the email is telling you is that an error might have occurred in box 12 when TurboTax imported your W-2. It's not anything that you did wrong.
There are a lot of different things that can be in box 12 of a W-2. Each entry in box 12 is identified by a one- or two-letter code. Some of them might affect your tax return and some are just informational. If the box 12 entries in TurboTax match your W-2 then it was imported correctly and you don't have to do anything. If they don't match, then depending on what the entries are, you might have to amend your tax return.
