Andreas, thank you for responding. I am using EcoInvent 2.3. When I click on a DB and want to import another DB, I get the first window, where I select either importing into an existing DB or as a standalone. When I select the former and select the file, I get a new window. I cannot click "finish" there or any other.
I found a work around. I can close the previous window and then can access the new one and actually incorporate it.
The reason why I was doing this, was to incorporate processes that are not present in the ESA database, e.g. internet use (relevant mostly during early phase space mission design). It did work now, but apparently requires a lot of memory.