I couldn't log into one of my servers through SSH with putty!....
But I could make a telnet.
So I diged a little for the cause and it just occurred to me that the version of putty I had in this computer might be an old one without support for SSH-2.
And indeed I was right.
I upgraded the SSH server just to talk in SSH-2 in order to be away from an exploit that can be done with certain versions of the SSH server when talking in SSH.-1
Well, that's a relief!