We have removed the AjaxControlToolkit reference as it is no longer required from our solution. However, one file, where no changes were made, is now breaking, after we removed the AjaxControlToolkit package. This file uses the Telerik RadCalendar control and is breaking during initialization.

Interestingly, the error disappears when the AjaxControlToolkit package is re-added. The following error is noticed when toolkit package is removed ,

Uncaught TypeError: Cannot read properties of undefined (reading '_events') at Sys.UI.DomEvent.addHandler (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:6:57366) at Telerik.Web.UI.RadCalendar.initialize (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a59462f1%3aa51ee93e:109:8) at Telerik.Web.UI.RadCalendar.endUpdate (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:6:53689) at Sys.Component.create (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:6:55151) at :4:5 at Sys._Application.add_init (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:6:67025) at :1:17 at Sys._ScriptLoader._loadScriptsInternal (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:15:4736) at Sys._ScriptLoader._loadScriptsInternal (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:15:4794) at Sys._ScriptLoader._loadScriptsInternal (Telerik.Web.UI.WebResource.axd?TSM_HiddenField=ctl00_rsmMain_TSM&compress=1&TSM_CombinedScripts=%3b%3bSystem.Web.Extensions%2c+Version%3d4.0.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a4533c2d0-c52e-4b49-a697-806d77e9914d%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2021.3.1111.40%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3abcb430ee-771a-4d39-a6d4-3550d81a8d67%3a16e4e7cd%3a365331c3%3a88144a7a%3aed16cbdc%3a24ee1bba%3ab2e06756%3a92fe8ea0%3afa31b949%3ac128760b%3a19620875%3a874f8ea2%3af46195d3%3a4877f69a%3a33715776%3a490a9d4e%3abd8f85e4%3a58366029%3a2003d0b8%3a1e771326%3aaa288e2d%3a258f1c72%3ae330518b%3ac8618e41%3ae4f8f289%3a1a73651d%3a333f8d94:15:4794)