Apparently the code is without errors, but running the page in debug mode, you receive an error like this:
By clicking on the button “Stop”, I’m going to try to understand what might have happened, and I realize that the object “_form” of the page does not exist, or is “null”
Needless to tell you how long I spent trying to figure out what could have happened, and where could be a possible error, of course without success.
After a meticulous search on the internet, I finally found an article that enlightened and saved me .
It seems to be a small bug of ScriptManager object, which misinterprets the tag <script /> without explicit locking.
It was sufficient change the tag and use the canonical syntax to solve it all:
End of the ordeal.