ASP.NET: RegularExpressionValidator Doesn't reCheck the input - asp.net

Question

i have a RegularExpressionValidator to validate an Email input that i have,
it works perfectly, if the input matches the Regular-expression,
However,if i enter a mistaken email it would show an error msg, if i fix the email in the input , it doesnt recheck it, the error msg stays not allowing me to click the Registeration button-or more like it gets clicked, but no event gets fired-
EDIT: added the ASPX code
< table width="100%">< tr><td>Username:</td>
<td>
<input runat="server" id="txtUsername" type="text" size="30" />
</td>
<td>
<asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server"
ControlToValidate="txtUsername" ErrorMessage="*"></asp:RequiredFieldValidator
<asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server"
ErrorMessage="Username has to be atleast between 4-8 "
ValidationExpression="[A-Z]{4-8}"
ControlToValidate="txtUsername"></asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td> Email:</td><td>
<input runat="server" id="txtemail" type="text" size="30" /></td>
<td>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"
ControlToValidate="txtemail" ErrorMessage="*">
</asp:RequiredFieldValidator>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server"
ControlToValidate="txtemail" ErrorMessage="Format must be: abc#abc.com"
ValidationExpression="^[A-Za-z0-9._%+-]+#([A-Za-z0-9-]+\.)+([A-Za-z0-9]{2,4}|museum)$">
</asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label runat="server" ForeColor="red" ID="lblerror"></asp:Label>
</td>
</tr>
<tr>
<td>
</td>
<td>
<asp:Button runat="server" Text="Register"
ID="btnSubmit" Width="118px" onclick="btnSubmit_Click" />
</td>
</tr>
</table>

Answer 1

Are you checking for Page.IsValid in your btnSubmit_Click method?
Also your validation expression for username doesn't look correct, use a comma between your min and max lengths.
ValidationExpression="[A-Z]{4-8}"
ValidationExpression="[A-Z]{4,8}"