No fatted calf

[#1]

I wanted to check my old, free-online account because I had reason to believe an old friend might have tried to contact me on it.
My login and old password log me into the PlusNet website OK, but when I try to use webmail, I get one of the following:
If I login as firstname@lastname  I get  Unknown user or password incorrect.
If I login as lastname                    I get  ERROR: Connection dropped by IMAP server.
It's frustrating because I 'm reasonably computer-literate, but this just isn't working.

[#2]

Login is in the format of username+mailbox and associated password or just username & password.
One thing to check is the server drop down list is correctly set on free-online.