UBB.threads PHP Forum Software Community Forums UBB.threads Version 7/8 Support Problem when people Register

When people try to register in our BBS in this section:
Enter the following information to register a user on our community.

Login Name
Password (between 4 and 20 characters)
Verify Password
Email Address
Re-type Email Address
Display Name (between 2 and 16 characters alphanumeric only)

and they click on submit. This error message is generated:
We cannot proceed.
All of the required fields are not filled in.

Yet the fields are filled in! We have tried it ourselves.