I've upgraded my site http://www.powertownedistro.com/phpBB3 from 3.0.0 to the new 3.0.4 version.

Now my New User Registration page gives out an error when you click submit to create a new account.

I should add that all current accounts are able to log in and use the system.

The error is:
[phpBB Debug] PHP Notice: in file /includes/functions_user.php on line 1443: mb_ereg_search_init() [function.mb-ereg-search-init]: mbregex compile err: premature end of char-class

followed by

[phpBB Debug] PHP Notice: in file /includes/functions_user.php on line 1444: mb_ereg_search() [function.mb-ereg-search]: No regex given

and the registration page reloads with an error shown to user of:

The username contains forbidden characters.

When I tested it I used the username Sister and my system is set up for letters, numbers and spacer chars.

I've gone from the upgrade packages to the changed files package, then ultimately completely reinstalled with the 3.0.4 full install package. Same error every time. Tested in both latest updated FireFox and IE. My mysql database was upgraded with each step I took.

I was able to work around the issue with help of a forum person by changing the acceptable chars types to Alphanumeric and space.

If you really need the PHP version I can contact my host and get it. It is 5+ as it was that several months ago but they upgrade all the time so. Dito on the MySQL version.