TextBox Validating - Button Firing

[kafmil]

I am using the TextBox_Validating method to validate controls on my page which is working fine. The problem is that it doesn't fire if i change the text through code when another control is changed(ie change the text in textbox when a calender control changes value). The validating method fires if i click the submit button straight after this changing the text programmatically. When the validating method has been vinished the click event doesn't fire. Does anyone know how to fix this.
So basically I change the textbox.text when a calender control changes value, validating doesn't fire, then i click submit, the validating method fires but submit.click doesn't fire.

Any help would be fantastic.
Thanks