There is currently a bug in Boardmaker 7 that sometimes causes a conversion error when trying to download an activity from My Boardmaker through the Boardmaker 7 dashboard.
When encountering this error the first and best option to try is to sign out of both the Boardmaker 7 Editor and from the My Boardmaker website itself. Once signed out, sign back in and try again. This resolves the issue most of the time. If it does not, the next thing to try is uninstalling and reinstalling the editor.
If you are still having issues after trying those options please contact technical support for additional assistance.