I'm not seeing this problem here (Win 7 PC w/Firefox, iPad, iPhone) -- have you disabled cookies, added some sort of pop-up or ad blocker, or made some change in browser settings? Admittedly it can indeed be frustrating that all this stuff constantly changes. The help info here suggests there have been problems with at least one ISP:
Why can't I stay logged in?If you are a Direcway customer, this is a very common problem. Please contact the direcway customer support, let them know what has been happening, and request a different proxy server.
If you are not a Direcway customer:
Try going to
http://www.pbase.com/logout and hitting shift + the refresh button on your browser.
Then, log back in with your username and password.
If that does not help, check the settings on your browser and any protection software you are running, and make sure you are accepting cookies (at least from pbase.com).
That's all I can offer,
DaveT