，请参阅AjaxControlToolkit.dll是否在bin目录中. 如果没有把它放到垃圾箱中，然后检查......

see AjaxControlToolkit.dll is in the bin directory or not.
if not put this in bin and then check......

您不是在指向正确版本的dll.
选中此 [ ^ ]网站进行相应的修订.

You are not pointing to the right version of the dll.
Check this[^] website for the appropriate revision.