Quite a few members have been caught out by this one recently, leading to the admins being sent anxious emails about being unable to access the mbs.
There is a security feature of these mbs which means that if you change your eddress in your profile at any point, the system will issue you with a new password.
This means that you'll be locked out of the mbs temporarily until you receive the new password. The system should send you an email with the new password automatically, so please do check your email for it.
So don't worry - it's just an automatic part of the board system.
LabRat