Question

I have two dropdownlists and I am filling one based on the other using javascript. In my javascript code I am calling for a webservice and with the results returned I fill the other dropdownlist. The problem is that after I have done that successfully the following error started to occur:

Invalid postback or callback argument. Event validation is enabled
using in configuration or <%@
Page EnableEventValidation=”true” %> in a page. For security
purposes, this feature verifies that arguments to postback or callback
events originate from the server control that originally rendered
them. If the data is valid and expected, use the
ClientScriptManager.RegisterForEventValidation method in order to
register the postback or callback data for validation.

Any idea ?

Answer 1

If you want to modify generated controls from client side, you have to disable eventvalidation or register all possible values with RegisterForEventValidation.
It’s well explained here.
It’s because the data sent to the client and received after by the server differs.

edit:also responded here.