Possible causes, are a corrupt program ini file or a corrupt project file try the following:
A program reset File, Settings, Reset program settings to default and restart the program, note: this will reset any custom settings eg folder paths etc
Locate and rename or delete the file videodeluxe.ini, it should be in
C:\Users\Username\AppData\Roaming\MAGIX\Videodeluxe version
If neither of the above work and when you re-open the project and the issue appears:
With the project loaded select File, Manage project, Export Movie file, Magix movie file (*.MVD)
Reset the program again.
Start a new project, then select File, Manage project, Import Movie file, Magix movie file (*.MVD) and load the saved .MVD file.