API returns UnknownError when executing euca-add-keypair in RHEL6

Guan, thank you much for your report.
There was incompletness on wiki instructions. Andrey Brindeyev just corrected it. You should disable SELinux in /etc/sysconfig/selinux and reboot your system.
Please let us know if it solve your problem.

After I disabled SELinux in /etc/sysconfig/selinux and rebooted system just as Ilya Alekseyev said, the error disappeared.

Thank you, Ilya Alekseyev.

Hi there, I got the same error after installing openstack ,
I did follow the instructions form http://wiki.openstack.org/NovaInstall/RHEL6Notes, and the selinux was disabled. The installed nova-api version is

Name : openstack-nova-api
Arch : noarch
Version : 2011.2
Release : 10.el6
Size : 13 k
Repo : installed
From repo : openstack

Again, I could not add a new keypair, the error messages in nova-api.log are:

Unexpected error raised: Unexpected error while running command.Command: ssh-keygen -q -b 1024 -N -f /tmp/tmpMtQ3UI/tempExit code: 1
Stdout: 'Saving the key failed: /tmp/tmpMtQ3UI/temp.\n'Stderr: 'open /tmp/tmpMtQ3UI/temp failed: Permission denied.\r\n'
(nova.api): TRACE: Traceback (most recent call last):(nova.api): TRACE: File "/usr/lib/python2.6/site-packages/nova/api/ec2/__init__.py", line 321, in __call__
(nova.api): TRACE: result = api_request.invoke(context)(nova.api): TRACE: File "/usr/lib/python2.6/site-packages/nova/api/ec2/apirequest.py", line 150, in invoke(nova.api): TRACE: result = method(context, **args)(nova.api): TRACE: File "/usr/lib/python2.6/site-packages/nova/api/ec2/cloud.py", line 315, in create_key_pair
(nova.api): TRACE: data = _gen_key(context, context.user_id, key_name)
(nova.api): TRACE: File "/usr/lib/python2.6/site-packages/nova/api/ec2/cloud.py", line 68, in _gen_key
(nova.api): TRACE: private_key, public_key, fingerprint = crypto.generate_key_pair()
(nova.api): TRACE: File "/usr/lib/python2.6/site-packages/nova/crypto.py", line 110, in generate_key_pair
(nova.api): TRACE: '-f', keyfile)
(nova.api): TRACE: File "/usr/lib/python2.6/site-packages/nova/utils.py", line 173, in execute
(nova.api): TRACE: cmd=' '.join(cmd))
(nova.api): TRACE: ProcessExecutionError: Unexpected error while running command.
(nova.api): TRACE: Command: ssh-keygen -q -b 1024 -N -f /tmp/tmpMtQ3UI/temp
(nova.api): TRACE: Exit code: 1
(nova.api): TRACE: Stdout: 'Saving the key failed: /tmp/tmpMtQ3UI/temp.\n'
(nova.api): TRACE: Stderr: 'open /tmp/tmpMtQ3UI/temp failed: Permission denied.\r\n'

can anyone advise how to solve this issue?