The symptoms you describe indicate that not all persons are correctly linked to a family tree.

There may be several causes for this problem.

If you have for "Number of family trees" the option "single tree" selected in your parameters, make sure that the correct single tree is selected in the listbox below that option.
Close the parameters, go to the Family tree page and execute the task "Assign family tree". This should assign all persons in your database to the on family tree.

If you have for "Number of family trees" the option "multiple tree" selected in your parameters, make sure that all trees you want to use are published and have the correct tree holder (family tree page).
Execute the task "Assign family tree". This should assign all persons in your database to the published family trees.

If this does not solve your problem, you may have to go to the menu module and open your Joaktree menus, check that the correct family tree is selected and save them again. Version 1.2 (and 1.2.1) deal slighly different with the menus.
Since you created the menu items for an older version, by "recreating" them (that is: opening and saving them) any problems should be solved.

Hope this solves your problems. If not, please, contact me again through this forum or at naastniels@gmail.com

Yes this occurred to me to. Did the proposed steps again to be sure, but still the same.

Since i have only 1 family in use, i use in my menu items the persones with whom i like the tree to begin. This has always worked well. Just to be sure i selected the one family in a newly created menu, also getting same error backend. The new menu was saved, but not functional.

You wrote "I'm processing some 100 new names ".

Does this means that your GedCOm only included the 100 new names?
If so, and the above suggestions do not help, try to upload a full GedCom file with all names. Perhaps the relationships between some family members are not set correctly.
If this is the case, this is a bug and I will have to look at the source code.

I use only one gedcom file with all persons including new and altered persons.

Just before the error occured i had on top father - son. I missed that the father was actually the grandfather, so i deleted the relation, added papa and made new relations. In Aldfaer al was ok. After uploding and processing the new gedcom i noticed frontend i had 2 papa's when selecting grandfather. So i checked backend and saw only 1 papa.

Just to be sure that someting had not gone wrong exporting the gedcom i uploaded the same file in Myheritage and it processed well.

Also i deleted all notes in preferences before exporting gedcom, uploaded, processed, but no luck.

So, i'm stuck for the moment. Maybe uninstall, delete tables and install again?

I recommend that you not delete the tables but empty the tables with exception of the following four tables
- joaktree_admin_persons
- joaktree_display_settings
- joaktree_registry_items
- joaktree_trees

Then reload the full gedcom file.
This should do the trick, I think. The fix you made in Aldfaer was probabbly not fixed in Joaktree. By starting with empty tables (specially the relationship tables) the relationships should be ok in Joaktree too.

has done the trick!

tnx for the quick resonses!, Roel