That's really strange. The error message you posted indicates that there is no database existent. A quick search on the developer forums leads to the only hint so far that this error usually disappears after reinstalling the app (and deleting the folder ~Library/Containers/Stage Traxx 3
(Caution, this will delete your data)).
After that the error usually will not come back. But I have not found a cause for this issue yet. What macOS version are you 2 on?