you have outgoing firewall enabled? if you disable it, updates work?
What I was doing, in order to get updates to work, was to effectively disable all the IPS rules. (Then re-enable after the update was run). Still, sometimes it pays to read the IPS logs. The logs were telling me that rule 2013504 was being invoked (which relates to Linux APR pkg management, and was enabled by default).
I found that particular rule and disabled it (leaving all other enabled) and it now works...
For other people using/updating Linux through an Endian appliance, take note of that rule, and the one immediately after it (which relates to YUM pkg management) if you have issues updating. You'll find both of them under "Auto Emerging Policy Rules".