git - Server host key not cached

Question

I try to push changes from my local repo to a remote repo. When I type:

git push origin

I get the following error:

The server's host key is not cached in the registry. You
have no guarantee that the server is the computer you
think it is.
The server's rsa2 key fingerprint is:
ssh-rsa 2048 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx
Connection abandoned.
fatal: The remote end hung up unexpectedly

How can I solve this? I'm using git from the command line in Windows 7.

Edit

When I try to do a simple ssh

ssh user@hostname

I get the following error:

Could not create directory '/c//%HOMEDRIVE%%HOMEPATH%/.ssh'.
percent_expand: unknown key %H

Somehow it will not create the directory, because the path is invalid. How to fix this?

@eckes: Edit2

My Home is set to %HOMEDRIVE%%HOMEPATH% is this correct?