Same here! Just get a red square and asks to put the correct details in..I asked for a new password and they sent me a 4 digit code to change my password, still can't log in with the same problem.
I'm having exactly the same issue, looks like a fault on the BT server affecting certain accounts. They are aware of the issue and are working on a fix I believe.
I have the same problem. I don't know which add ons you are using but I have found that if I temporarily disable McAfee WebAdvisor it works fine.
Note: this is the same add on that comes with the McAfee anti virus software supplied by BT. Ironic that it only appears to be affecting BT email and MyBT whilst all other websites appear unaffected !
I'm hoping BT will fix this soon but who knows?