From telnet try "config t, crypto key generate rsa"
if that doesn't fix it, you might be running 8.2.3 or 8.2.4 code, I've seen SSH stop working in one of them for no reason a couple of days after reboot. Change code.
You might ned to do the follwoing:
++do "sh run ssh"
copy the ssh config.
erase it config and re-apply
++ generate cryto keys again
crypto key generate rsa modulus 1024
++ Reboot the firewall
If you are running 8.2.3, this would re-occur after a fauilover happen, so code is really imp. Let me know the code you are running.
this is a prod box
can't reboot right now.
will schedule it for the maintenance window
is there any command to restart the SSH daemon or process?
Are you able to ssh to other interface or is it happening for all the interfaces, beacuse there are some issues with ssh on 8.4.1. Since it is a prod box, I woudl suggest you to Open a TAC case for it, to identify the correct cause for it.