... yesterday i decided to save it as a Singleplayer mission: Result: The mission begins with a error messages (can not find xxx.jpg / xxx.sqs), and some scripts (the one in the folders) are missing...
I did not understand exactly what you did with your folder
Did you use "Save as SP Mission" in the editor? That function only moves the root-folder of the mission including the mission.sqm to OFP:s missionfolder. All other files (scripts, sounds, briefing, overview, etc) must be moved manually.
Solution: open explorer, copy the entire folder (with all subcategories) from c://programfiles/operation flashpoint/users/USERNAME/mission/MISSIONNAME and paste it into the OFP missionfolder c://programfiles/operation flashpoint/missions
Now it should work ;D
If you use separate subfolders for pictures and scripts you must include the folder name in your path when you call a script or directs the overview to a picture, but since your mission works in the editor I suppose you already did this.