How Can I Validate Not All Letters But Numbers In Asp.Net?

All Numbers can be allowed
A number can have zero or more digits in front of a single period (.) and it can have zero or more digits following the period. Perhaps: [0-9]*\.[0-9]* will do ...

A number may not contain a period at all. So, revise the previous expression to:

[-+]?[0-9]*\.?[0-9]*

At least one letter allowed
Basically this means:
Zero or more digits;
One alpha character;
Zero or more alphanumeric characters.

^\d*[a-zA-Z][a-zA-Z0-9]*$ 

No All Characters Allowed
Explanation:
^ matches the start of the string.
[A-Za-z]* matches 0 or more letters (case-insensitive) -- replace * with + to require 1 or more letters.
, matches a comma followed by a space.
$ matches the end of the string, so if there's anything after the comma and space then the match will fail.

^[A-Za-z]*, $

Ex:

<asp:TextBox ID="txtName" runat="server"/>
    <asp:Button ID="btnSubmit" runat="server" Text="Submit" />
    <asp:RegularExpressionValidator ID="regexpName" runat="server"
                                    ErrorMessage="This expression does not validate."
                                    ControlToValidate="txtName"
                                    ValidationExpression="^[A-Za-z]*, $" />

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