On line 2920 of the webloginpe.class.php file you can replace the eregi regular expression with the new PHP filter_var() function (PHP 5.2). If you have an older version of PHP you'll need to replace it with preg_match and modify the regular expression accordingly.
function ValidateEmail($Email)
{
// Original: ^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$
//if (!eregi("^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,7}$", $Email)) // pixelchutes
if(!filter_var($Email, FILTER_VALIDATE_EMAIL)) // sottwell
{
return $this->FormatMessage('The Email address you provided does not appear to be a properly formatted address.');
}