ssh_keygen : command not found

[Ron Leach <ronleach@tesco.net>]

I hesitate to trouble the list with this but, when trying to generate 
a key pair on a (lenny) system recently upgraded to wheezy, 7.7, I am 
seeing this:

ron@d7server:~$ ssh-keygen
-bash: ssh_keygen : command not found
ron@d7server:~$

Aptitude says that openssh-client, version 1:6.0p1-4+deb7 is installed 
and, from its description, includes the ssh-keygen utility.

~/.ssh exists, and does not contain a key pair.  It does contain an 
authorized keys file.

Openssh-server is installed and runs, allowing remote login via rsa key.

Nothing in wiki suggests that ssh-keygen is not the correct command, 
nor do the man pages, in fact all the documents seem to suggest it 
should run.

Maybe I could check it is actually present.  Where does ssh-keygen 
live in the machine?

I can't think what else to try, and would be grateful for any 
suggestions.  (Don't hold back, I don't doubt I've done something 
stupid :( )

regards, Ron