access to ameritech email through gmail

Are you using gmail's Accounts and Import/Check mail from other accounts to do that?

Can you even log into the att/yahoo ameritech.net webmail directly? 

I recommend you disable the gmail fetch and change your ameritech.net webmail settings to forward to your gmail account instead (assuming you can even log in).  It's usually more reliable and timely too.  In the past, when I tried using my email account (not gmail) to fetch email from my att account I found it unreliable in that the periodic fetch failed about 30% of the time (that's a guesstimate).  I would get an error report instead.  It would eventually successfully fetch in one of the future periodic fetches, just not every time.  It might be gmail doesn't report the fetch failures and just waits for the next fetch cycle to try again.   Not sure why this behavior occurs only with the yahoo servers. 

If you don't want to change to forwarding, and you can still log into your account just to check the login info still works, then all I can suggest is wait.  Maybe eventually it will start working again.