Hi there!
I had to install your great module onto a server that could not provide the ctype_* functions.
So instead of flushing your module, I created both needed functions for it to work.
Here's the code snippet (I added it at the top of your .module file) if you wishes to include it in your future development branches.
Have a nice day!
Benoît

if (!function_exists('ctype_alpha'))
{
function ctype_alpha($str)
{
return preg_match("/^([a-z])$/i", $str);
}
}
if (!function_exists('ctype_digit'))
{
function ctype_digit($str)
{
return preg_match("/^([0-9])$/", $str);
}
}