Sometimes problems like this are related to the web browser/ADTRAN interaction. Try clearing the browser cache and cookies. You can also try another web browser. What version of AOS firmware are you running?
Sorry, had forgotten that I had this thread...
Ended up fixing it by 1 line of config.
Config had the line 'no http server'.
Removed the no from the line of config and could then get on.
Not sure why the change in firmware would have disabled the web config.