cant save "Level Blueprint is in another map"

need help i get an error massage when i try to save…

Can’t save …/…/…/…/…/…Unreal Projects/Prototype/Content/Blueprints/MainMenu.uasset: Graph is linked to object(s) in external map.
External Object(s):

Try to find the chain of references to that object (may take some time)?


The asset ‘/Game/Blueprints/MainMenu’ (MainMenu.uasset) failed to save.

Cancel: Stop saving all assets and return to the editor.
Retry: Attempt to save the asset again.
Continue: Skip saving this asset only.

after hitting continue

The following assets failed to save correctly:

this error only occurs when i reference my level blueprint in my other blueprints. thank you for your time hope you can help