The ajax toolkit does not use , nor require the "older" toolkit script manager.
Since for quite some time (toolkit version 15????) the ajax toolkit now uses the standard asp.net script manager.
You don't want to use, nor require the older ajax script manager. So, on that page, remove the ajax script manager you have, and then drag + drop in the standard asp.net script manager. This one:
So, in above, I am using the ajax toolkit AjaxFileUploader as the designer screen shows. However, note the name and the script manager used in above. You are to now use the standard asp.net script manager, and avoid using the older ajax script manager.
In fact, you should not see, nor find the older deprecated ajax script manager in the AjaxTools box anymore.
The above screen shot does not show all of the ajax toolkit controls, but for considerable time (about 10 years now), the aj toolkit does not require nor include the aj script manager.
This was perhaps one of the "best" changes to the aj toolkit, since now pages don't need 2 script managers, and you don't require use of the aj script manager anymore (it was a pain point for pages, since only one script manager was allowed, and the aj script manager was not 100% compatiable with the asp.net one).
So, if you recent downloaded (in the last 10 years) a newer version of the aj toolkit, then you not need nor find nor should use the deprecated aj script manager.