Was having the same issue, but got it resolved.
1. #configure-network
after this, check if the support assistant is able to reach the vc (#ping vcenterserver).
2. Make sure the support assitance is able to connect to vc.
#wget https://vCenter
Then try to register, if there is any error, reboot the support assistant and run the same command to see if its able to make a connection.
2. Make sure that support assitance is able to connect to https://supportassistant.vmware.com
#wget https://supportassistant.vmware.com
--2013-02-06 08:03:58-- https://supportassistant.vmware.com/
Resolving supportassistant.vmware.com... 208.91.2.34
Connecting to supportassistant.vmware.com|208.91.2.34|:443... connected.