When creating a SharePoint Control with a ControlSrc pointing to a user control (for example to replace the SmallSearchInputBox), you might get an error in the ULS log saying that the control cannot be found in ~/_controltemplates/<name_of_usercontrol.ascx> although the file exists in the correct directory. This happens when using SharePoint 2013 and forget to add the correct SharePoint version to the path. In our case this should be

~/_controltemplates/15/<name_of_usercontrol.ascx>

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