I am having a similar problem.  The W-2 amounts are wrong for some,but not all employees for Fed W/H, Soc sec, and medicare.  State taxes are correct.  The employees involved vary by each type of W/H.  Been on hold for support for 1 hour and 54 minutes and counting to get help.  I can manually correct the amounts, but why the problem to begin with and what other problems could there be?

i was having a similar problem on one of my network computers (the one we use to print w2s)..  SO, there was a 2nd July 2020 payroll tax update.  I did the first July payroll tax update timely, and the January 2021 one timely, but somehow did not dload the second july 2020 one...even when it kept popping up when i closed Sage,  Because I just assumed the Jan 2021 would override all of the July stuff.  Even my 941s on that  computer did not agree with the ones on my server.  So, on that computer,  I had it install the second July update, then checked for updates and installed the jan 2021 one again.... and everything is fine.  Except, I still have to rename the company on some of my clients to get the covid pay popup to open when I start printing 941s.

Reinstall the January payroll tax update, even if the Help > About Sage 50 Accounting screen already shows that it is installed. I ran into two cases of this today.

What is the process to reinstall the January payroll tax update?

Close Sage 50. Go to the Updates folder in your Sage 50 data path and double click the file Tax2021Jan_Release2021.exe (depending on your Windows settings you may not the the ".exe"). Then just follow the prompts to install.

If you don't know where your Sage 50 data path is, the easiest way to find it is to open your company in Sage 50, go to the Maintain menu and choose Company Information. There is a greyed out field named Directory. It will show the location of this company, for example "C:\Sage\Peachtree\Company\yourname".

In that example the data path would be "C:\Sage\Peachtree\Company\" so you would find the Updates folder inside the Company folder.

I went to the location you show and my file name for the update you reference above was Tax2021Jan_Release2020.exe.  You show the file name has Release2021, but mine has Release2020.  The file date is 12-20-2020.   

I actually had found the file prior to seeing your response and went to install it (first I did a backup).  I got an error message that said "The latest Sage 50 Accounting service release is not installed on your computer. You must install the service before running the Sage 50 Payroll Solutions update."   So I was unable to reinstall the update.  I do have Sage 50 Premium Accounting 2021 SR-1 installed according to my About Sage 50 screen

Just correct the information manually.   Not sure why it happens, but it does.  Good for you for verifying your information.

LOL.. yeah.. just correct each of the p/r FICA, MC, and WH on  every client, even if that client has 60 employees or so.  SMH!.  Yeah, that's some solution...hardly a 'Best Business Strategy"

Sorry, I didn't write the program.  I was just telling you how to fix it.  If you don't make changes after the fact or you use the button at the top of the paycheck to correct the check, you usually don't have errors on w-2's.  

If you have 2021 SR-1 installed, then try manually downloading Tax2021Jan_Release2021.exe here and then double click the file to install it.