WCCP negotiation issues can occur when the following elements differ between the ProxySG appliance and your WCCP network devices:
WCCP Service-Groups must all use the same Assignment Type.
All Assignment Type configuration settings must be identical on all devices within the WCCP Service-Group. Any changes to any device in the group will cause that device fail to negotiate to join that service-group.
For example, if you have four ProxySG appliances in a Service-Group and if you change the assignment type from Mask to Hash, you must modify the assignment type on all ProxySG appliances.