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

Further information:

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"