Regarding the Andy's question:
Could you please try following this steps and let me know if the issue still persists:
1) Close the Visual Studio.
2) Stop the IIS if the site is deployed on it.
3) Close all other programs that eventually use “bin\Telerik.Web.UI.xml”
These 3 steps are to ensure no one is locking the file for writing.
4) Check the security of “bin\Telerik.Web.UI.xml”, to make sure you have write permissions.
5) Now copy “...\Telerik.Web.UI.xml” to the “\bin” folder of your project.
Regarding the Mike's question:
The Telerik.Web.UI.xml keeps the documentation of the assembly. It could be used in tools which generates documentation files.
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