In case you have enabled the RescueSystem and want to log in:
Since the RescueSystem contains an own SSH server the SSH key differs. This in indicated by the abovementioned error message.
This StrictChecking can be temporarily switched off with:
ssh -o StrictHostKeyChecking=no IP address
This message just indicates that the servers SSH key has changed. This may have the following reasons:
- The server has been reinstalled
- The RescueSystem has been activated
- You regenerated the keys on the server
- Due to a compromising of the server by acquaintances and / or strangers
- "Man-In-The-Middle Attack"