Error Encountered When Inserting <>

A potentially dangerous Request.Form value was detected from the client (newstable: _ctl0: TextBox="<#br>"). Description: Request Validation has detected a potentially dangerous client input value, and processing of the request has been aborted. This value may indicate an attempt to compromise the security of your application, such as a cross-site scripting attack. You can disable request validation by setting validateRequest=false in the Page directive or in the configuration section. However, it is strongly recommended that your application explicitly check all inputs in this case.
I stumbled upon this error when i tried to insert '<#br>' into textbox, and the solution to the error was to include: ValidateRequest="false" in the beginning of the page, after "< % page ".