If you follow the instruction here:
http://wiki.centos.org/HowTos/FreeNX
You will get an error message from NX client:
The nx service is not available or the nx access was disabled
To fix this, connect to your SSH and type:
cat /var/lib/nxserver/home/.ssh/client.id_dsa.key
Copy the text you get and in your NX client, on your login dialog box go to:
Configure… > General Tab > Key
And paste the text there and you will be fine

I'm a programmer at 
Thank you so much for this.. I was baffled for a little while
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I was baffled too, and still sorta am- because I thought this could do password based authentication negating the use of a key. But whatever, at least its working.
Thanks
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thanx for posting.
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This is really a HELP!!!!
Thanks a million !!
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Thank you so much !!! You are a genius !
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thank you ! you help me .. sigh
thx so alot
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That’s really great..Thanks a lot this is really helpful
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Thank you very much for that suggestion !!!
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In my case was: /usr/NX/share/keys/default.id_dsa.key
and works fine!
thanks!
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Thanks a million
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this was my case,too:
cat /usr/NX/share/keys/default.id_dsa.key
and it worked as well, thanks!
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Thanks alot!!
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works fine!
thanks!
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tnx alot ,works great
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