Regular Expression fails in IE, but works in Chrome and Firefox?

I have the following asp.net markup:

<asp:TextBox ID="txtPassword" runat="server" TextMode="Password"   
ValidationGroup="passwordValidation"></asp:TextBox>

<asp:Requi开发者_JS百科redFieldValidator ID="RequiredFieldValidator1" runat="server" Display="Dynamic"
ControlToValidate="txtPassword" Text="Required" ValidationGroup="passwordValidation" />

<asp:RegularExpressionValidator runat="server" ControlToValidate="txtPassword"  
Text="Passwords should contain a minimum of 7 characters with at least one numeric 
character." ValidationExpression="^(?=.*\d{1})(?=.*[a-zA-Z]{2}).{7,}$"  
ValidationGroup="passwordValidation" Display="Dynamic"></asp:RegularExpressionValidator>

If I type in a password like test1234, it passes in chrome and firefox, but the message that my password should contain a minimum of 7 characters with at least one numeric character is shown in internet explorer

You're probably getting bitten by the infamous IE regex lookahead bug. You should be able to work around that by making the length check a lookahead like the other conditions, and putting it first.

^(?=.{7,}$)(?=.*\d)(?=.*[a-zA-Z]{2}).*

But I think I see another problem. (?=.*[a-zA-Z]{2}) matches two consecutive letters; is that really your intent? If you want to require at least two letters, but not necessarily consecutive, you should use (?=.*[a-zA-Z].*[a-zA-Z]).