When I run ktutil list, I get a list of several clients. However, when I run kinit for any of the listed clients, I always get client unknown. Any ideas?
The KDC(s) you're communicating with doesn't have any records for the principal you are requesting. This could be for a couple of reasons.
Did you check any of these things or try anything else before asking? Your question demonstrates no effort by you to solve your problem. This isn't to say that you haven't taken any steps to solve it, just that it is impossible for any reader to know if you have done so.
Can you acquire tickets for at least one principal of that realm?