extending a circuit

[Robert Hogan]

i've verified a server is up by doing:

getinfo desc/all-recent

and

getinfo network-status

it's listed in both. yet when i try to use it to extend a circuit:

extendcircuit [circid] [servername]

it tell me '(waiting for keys)' and then the circuit fails.

any idea what i'm doing wrong? what is the definitive way of deciding that a 
router is available for circuit extensions?

thanks,
robert