18 Jul 2012
29 Nov 2011
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As tim mentioned, the Telerik.Cms.dll is a library from the Sitefinity 3.x version.
Adding it to a 4.x website will likely not resolve your issues, as instead you need to update your code/control to use the new 4.x api and libraries.
If you need help with this, please feel free to post more details about your scenario and I'll be happy to help!