When upgrading the version of ArcGIS Desktop or ArcGIS Server without first uninstalling the ERDAS ECW for ArcGIS Plugin, it will stop the ECW Plugin from working. In this case the user will not be able to install a newer version of ECW Plugin and the previously installed version of the ECW Plugin will not uninstall.
If you are upgrading an installation of ArcGIS Desktop or ArcGIS Server, you must uninstall the ECW Plugin first, then after upgrading to the newer version of ArcGIS Desktop or ArcGIS Server, install the corresponding version of the ECW Plugin.
If the above steps were not followed, older version of ECW Plug-ins will not uninstall. In that case you will not be able to install the newer version of ECW Plug-ins. Please do the following to overcome this problem: