Vista - New Problem: Requires I type in ID and password each time I log

This problem just began happening today, but every time I open my email, I
get a message that says, "Logon to pop-server.satx.rr.com. Please verify
that both the username and password are correct for your mail server.

It then has two boxes to type in the username and password.

There is another box that asks the user if we want the credentials to be
remembered. I have that box clicked. I log on and everything works fine.
If I close and reopen the email, I still have to log on again. This has
never happened before. Does anyone have any solutions?? Thanks in advance.