If you import a solution to a vanilla environment with readonlygrids, the import currentlfails because it says it can't find a form. Investigating, it's card forms that are already in the solution file. So you have to edit the customizations file, remove all occurences of
CardForm static="true" type="Form.Card">blablabla
Import the solution without those lines, and when the import ends import it again with the deleted lines.