It misses the AjaxControlToolkit.dll in the bin directory after you deploy the site.
Please fix this by following these steps:
- Get AjaxControlToolkit via http://ajaxcontroltoolkit.codeplex.com/releases/view/43475
- Add AjaxControlToolkit.dll to your Reference folder(Right Click on Reference Folder > Add Reference > browse AjaxControlToolkit.dll).
- Set Copy Local to True
- Publish your site.