WAD: Layout control is not properly installed

After installing SAP GUI 7.30 the BEx Web Application Designer does not work anymore. It just crashes after opening a WebTemplate.

After installing BI Frontend Patch 300, the WAD gives the following error message when opening a Template: "Layout control is not properly installed"

Already tried to uninstall and reinstall the Front-End with all patches, but it doesn´t work...

Any idea?