This problem is expected if more than one person is working in the same project folder. One instance of Visual Studio will lock the binaries (Telerik.Web.UI.dll) and you will not be able to modify (rebuild) them from another instance. The workaround is for each person to have a copy of the project on their own computer and if you want to keep changes in sync, use a revision control system (source control). There is nothing that we can do to fix the problem from our side, since this is not related to the Telerik.Web.UI.dll reference, but to Visual Studio in general.
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