Alfons,
Servoy only exports users that have a security relation to the solution you’re exporting.
Make sure that users belong to a group that has security settings (accessible/viewable) to an element or a form.
You can enforce group security settings by selecting the group, on the forms tab select a form or a named field in a form of your solution and press the update-button.
Now all users belonging to that group will be exported.
Rob