[Spacewalk-list] Cannot trtrieve reposiitory metadata (repomd.xml)

[YANG LI]

I got the latest spacewalk 2.2 installed. It was working fine. I can register a rhel6 client to oraclelinux6-x86_64 channel and did yum update without issue. Then one day i found out yum update is broken. 
this is message I see when I try to yum check-update:

[root at yangli-test ~]# yum check-update Loaded plugins: product-id, rhnplugin, subscription-manager This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. This system is receiving updates from ULN. Error: Cannot retrieve repository metadata (repomd.xml) for repository: oraclelinux6-x86_64. Please verify its path and try again

I have tried to resync oraclelinux6-x86_64 channels without luck. I am not sure which changes have caused this. I think there are only three changes I have made on spacewalk servers:

1. added EPEL channel as child channel of oralelinux6-x86_64 channel

# spacewalk-common-channels -v -u aais-admin -p spacewalk -a x86_64 -k unlimited epel6

2. added osad to force scheduled actions to run mediately on spacewalk clients. This was tested and worked fine.

3. Enabled monitoring.

I am thinking it may related to add epel channel, so i deleted epel channel, but it still broke. Any idea how i fix this?