When I am trying to change the duration of a sustaining gift, I get the error "Unable to change the existing duration of the gift because connectivity with a CRM is established. For proper synchronization with CRM, cancel this gift and create a new one with the desired duration."
This error is appearing because you have an integration setup, because of certain limitations with integrating the two systems you will need to cancel the sustaining gift and record a new one with the proper duration. Unfortunately this is a necessary limitation for both the LCRM and Raiser's Edge Integrations. However, if you have the Raiser's Edge integration the ability to change the duration of a sustaining gift may be added in the future -- this is being tracked in bug 68055. If you would like to be notified if/when this feature is added, please file a case with support to be added to the bug.