I have just purchased a Humax FVP-5000T and am getting the same problem signing into the ITV Hub as is being reported on the avforums website.
It would appear this issue has been going on for some time.
When trying to access the ITV Hub I am unable to Sign in.
After selecting 'Sign In' I get the screen:
'Whoops What's going on here? Retry, Manual Sign In, Cancel'
Selecting ‘Retry’ produces the same ‘Whoops’ screen.
Selecting ‘Manual Sign-in’ results in me entering my id and password but then the ‘Whoops’ screen appears again.
The box has been updated to the latest software.
I have tried powering off / on the box and the router and reset the ITV Hub but the issue remains.
I have no problem logging on to the ITV Hub on the Samsung Smart TV app so it is definitely an issue with the Humax box.
I have sent an email to firstname.lastname@example.org detailing the problem and would suggest anyone with the same issue does the same.
I'll post any reply I receive.