The AjaxFileUpload control does not work if it is contained in a page that is reached from another page via Server.Transfer. It appears to work correctly when reached via Response.Redirect.
Comments: This is the expected behavior. AjaxFileUpload control heavily utilizes client-side URLs that work relative to the page where the control is located. If you use Server.Transfer, this will break the logic of the control, as long as this method does not change the page URL where the control is located. Meanwhile, Response.Redirect will produce the correct results, because the page URL reflects the control's real location in the site hierarchy. As a general rule, it is better to avoid calling Server.Transfer if you have any client-side code on a page.
Comments: This is the expected behavior. AjaxFileUpload control heavily utilizes client-side URLs that work relative to the page where the control is located. If you use Server.Transfer, this will break the logic of the control, as long as this method does not change the page URL where the control is located. Meanwhile, Response.Redirect will produce the correct results, because the page URL reflects the control's real location in the site hierarchy. As a general rule, it is better to avoid calling Server.Transfer if you have any client-side code on a page.