Can't save file after deleting one model

I started with one model, then created a second and afterwards deleted the first one completely. Now I am unable to save the file and I also can't run any study. I think there are some variables left from the first model I deleted. Here is the error message when I try to save the file:

The object 'Type: Geometry
Tag: geom1
Dimension: 2
Current child: r3 is not contained in a resource.


In general, how can I access variables and delete them?