Problem in enable and disable the regular expression validation for textbox

Hi

I having a two radio button.

When the second radio button is enabled, a text box which accept the email id will appear.

I am validating the Email using Regular expression validater.

When the second radio button is clicked, and i enter the invalid email id so that it shows me and error.

But when i click the first radio button, it is  showing the save validation.

I need this to not show the validation when the first radio button is clicked and invalid email id is there in the text box.

Thanks in advance.