To avoid SolidWorks creating a circular reference, in an assembly environment you can only reference sketch geometry from one assy. If you were allowed to reference from two then the assy would fight against each other.
what i think has happened here is you created an assembly, created your in context references and then saved the Assembly. So the incontext links are referring to the unsaved name of the Assy (Assem1) to which you change with the first save.
it is best to create the assembly, save it, and then start your incontext modelling. then use SolidWorks Explorer if you need to rename things
Thank you very much for your answers.
I will tell you later by trying your answers. The computer is not with me.