Expinion.net Member Management System 2.1 - 'register.asp?err' Cross-Site Scripting

source: https://www.securityfocus.com/bid/9932/info
 
It has been reported that a number of Member Management System scripts are prone to cross-site scripting vulnerabilities. These issues are reportedly due to a failure to sanitize user input and so allow HTML and script code that may facilitate cross-site scripting attacks. The issues are reported to affect the 'err' parameter of 'error.asp' script and the 'register.asp' script.
 
Member Management System version 2.1 has been reported to be affected by this issue, however, other versions may be vulnerable as well.

In the register form: "><iframe src=http://www.example.com/admin/user_del.asp?ID=[ID to delete]>