I have created a login form with 2 textboxes, login linkbutton & register linkbutton which is invisible. When the user login fails the register linkbutton pops. I have set the validation control for the userid(which happens to be an email id). I have set the ControlToValidate property for the validator to the userid textbox. If the login fails, i want user to click the register button and go to the register form. But, because of the validator control it not going to the next webform. Unless blabla@blabla.com is given the userid textbox. WHAT SHOULD i do? i have tired to disable the textbox and the validator control. STILL not working.

You can omit validation by setting CausesValidation="False" to the LinkButton (declaratively). You can also set it in code, in case needed.

[C#] 
LinkButton1.CausesValidation = false;

[VB]
LinkButton1.CausesValidation = False