A small problem encountered when using ajax.net, the solution of "sending back or callback parameter is invalid"

Today, an error is reported on the page where ajax.net is used,
The prompt message is:

The callback parameter is invalid. Use <pages enableeventvalidation = "true"/> in the configuration, or use <% @ page enableeventvalidation = "true" %> On the page to enable event verification. For security purposes, this function verifies whether the parameters of the send-back or callback events come from the server controls that initially present these events.

No solution has been found for online search.
TheArticleThe reason is:
The article http://www.cnblogs.com/asp600/archive/2006/11/04/550216.aspx from: swordsman

So far, there are two situations:
First, form nesting. One page can only have one form. Check carefully.CodeYou can solve this problem.
Second, Ajax is used in the drop-down menu, which is common in the provincial/municipal linkage menu. It may be because the initial item value of the drop-down menu is assigned to the ASPX page. This error is prompted when the event is returned, delete the initial item value from the drop-down menu and add the item to the binding event.

Later, I discovered that the problem was not there.
The reason is that the value attribute of the listitem in the dropdownlist control contains Chinese characters. You only need to change the value to English or numbers.
There is another solution on the Internet: Set the enableeventvalidation attribute to false, but there is no warning box. The data still cannot be passed to the server, resulting in the selectedindex value being zero.

It seems that ajax.net has limited support for Chinese characters, or is it because you need to set the encoding in Web. config ??????