What is the version of Essential Tools you are using? Is this a new install or an upgrade from a previous version. I would think that there is a problem with the Syncfusion dlls in the Global Assembly Cache (GAC) on your PC.
Please locate the GAC on your PC (it is normally c:\windows\assembly or c:\winnt\assembly on Windows XP and Windows 2000 respectively) and make sure that only the latest version of the Syncfusion.tools.dll is present there. If there are more than one version of the file delete the older versions from the GAC.
Please try this and let us know. Thank you for your patience.