The located assembly's manifest definition does not match the assembly reference
Most probably the version of the RadControls you have installed in not the same as this one used in Sitefinity. Then the referenced assemblies version has been changed and the application cannot find the correct dll. Check the project references and check your GAC to see what version is listed there. This Microsoft article states that assemblies found in the GAC are not copied locally during a build, so you might need to remove the old version before doing a rebuild all.
You can use the fuslogvw.exe
application that ships with Visual Studio to get more information about the binding failures.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.