Urgent Blocker! I can't save because "The file contains external references from other teams"

[c.schmidTXJCD]

Sorry that the screenshot is in german, I posted it in the german forum a couple days ago but didn't get an answer so I try it in here.
Saving always worked normally and I didn't add any additional external references since i saved last time.

Please help me! Our project is standing still since two days now because of this bug.