customvalidator problem

Hi,
I have a customvalidator inside an update panel, every thing is inside a user control.

The proble occurs only on the production server,

When I put a value that s more than 3 chars the customvalidator is valid and my page posts back without a problem.

Then I remove that entered text, so the textbox is empty and therefore not valid, when I click on the submit button, my error message is not displayed, which is not normal. the CustomValidator should be invalid and the error message is supposed to display since no text is entered in my textbox.

Now here is the weird part:
All this, I mean the customvalidator works fine on my developement computer, it only acts weird on the production server.

Also, on the server the validator works fine the first time the page is rendered, it s only when the page is postback that thnigs start to be crazy, the first time it renders, if the textbox is empty and I click submit button the error of my customValidator is displayed.

Sorry if my email is so redundant :)

I just made a litlle verification and wanted to add that when I remove the Updatepanel, the customValidator works appropriately, so how can I fix the problem and keep the updatePanel at the same time on my page?
Thank you