The provided code snippet is not enough to determine the exact cause of the issue.
By design, RadFileExplorer does not use RadToolTip, which makes me believe that the compilation warming message is not caused by the explorer. Could you please verify that you are not using the obsolete property mentioned in the error message somewhere else in the project?
If not, could you please open a formal support ticket and provide fully runnable sample project reproducing the error, so we can examine and debug it locally?
the Telerik team
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