Got this error while a script was building an RPM:

RPM build errors:
Unable to open temp file.
error: Unable to open temp file.

Turns out the permissions of /var/tmp were wrong. I did a 'chmod 777 /var/tmp' and 'chmod +t /var/tmp' to fix it. You can check what rpm's tmp dir is by running 'rpm --eval %_tmppath'.
-Paul