As I replied to Doug, I _am_ importing this xml into a blank new tree. I had a question about whether using my original .gramps in my original home directory was confusing the new version of gramps, so I removed that directory and repeated the import. It gets the same error messages and has the same problems. I have now checked the xml file that gramps 2.2.10 produced and indeed, every one of the families in error is duplicated in the xml file ( the family stanza is duplicated entirely). I guess my only recourse is to edit the file and remove all these duplicates (ouch!).
I still have the problem in 3.1.1 where creating a family (adding a partner) is _not_ generating a new family id (it comes up blank and I leave it blank) and gives me the error
"You have attempted to use the existing GRAMPS ID with value None. This value is already used. Please enter a different ID or leave blank to get the next available ID value"
This is serious, None should not be allowed as an id, it leads to all kind of troubles as some code cannot handle it. When None is given, it should automatically assign a new value instead. My guess is there is a family with id None in your tree, and that causes the problem. Sort on that column in family view, and see what it is, then delete or assign a valid id. If this crashes, you will have to do this in the xml then import....
I fixed a bug in 2.2.6 or so that could create empty id's, perhaps it comes from there. Often when bugs are found that can cause serious issues, the check and repair tool is also updated to clean the old errors out. Not always though...
You should indeed edit the xml file to remove the wrong families. You can also just change one letter in the handle of the familyy, and GRAMPS will consider the duplicate another family. You will have to then delete duplicates after import (but you have the ids already from the first import ).
Should you with the present version be able to make duplicate families, or objects with empty id's, please post a bug report.
Note that running the check and repair tool, and the remove unused objects tool, might fix some things in 2.2.10 and 3.x