I see the channel sles11-sp4-ltss-updates-x86_64 when I run mgr-sync list channels but when I try to add the channel, it says "Channel is not mirrorable: sles11-sp4-ltss-updates-x86_64". I managed to add other channels like sless11-extras-x86_64-sles-sp4 using command line so I think my credential is working.

@Philip