Apply minimum length validation using ASP.NET Validation Controls

Validation expression should be : /{numberOfCharacters}/

Comma indicates at least number of characters, no comma indicates exactly as much characters

<asp:RegularExpressionValidator
ID="revNewPW0"
runat="server"

ControlToValidate="textNewPassword"

ErrorMessage="Password should have at least 7 characters"

ValidationExpression="/{7,}/"></asp:RegularExpressionValidator>

Even better solution is here:

http://forums.asp.net/t/1130081.aspx