Can't log in any more - "Wiki names must be at least 4 characters"

I have used my pbwiki quite happily for a fair while now but suddenly I am unable to get to it. Without giving the exact name, it has only 3 characters before the .pbwiki.com
Now, when I enter the address it redirects me to https://my.pbwiki.com/?return_to_page... and wants me to log into this. If I enter the wiki name in the "Enter your wiki name" box it returns "Wiki names must be at least 4 characters".
I signed up for a my.pbwiki.com account but this made no difference.

I would happily change my wiki name to something 4 characters or more if I could get into it!

Any suggestions welcomed.