Problem solved:
on an old harddisk i found the demo V3.0.0.0
After disinstalled V3.0.42.0 i installed the demo V3.0.0.0. After that i copied my full-version V3.0.0.0 over the demo-files. All the problems are gone: no more grids in the component tray, all the grids are selectable in the project, after rebuilding the project the columns in the grids aren't gone.
I think it is wise to add the demo V3.0.0.0 to the downloadsection at the site because the demo V3.0.42.0 isn't compatible with the full version V3.0.0.0