B757 Captain reports returning to the gate after taxi out for a planned maintenance ferry flight. Dispatch and Maintenance Control cannot agree on the legalities of the flight due to recent changes to maintenance and flight manuals. After some discussion the flight departs as planned.

Narrative

Our aircraft had a problem with uncommanded fuel transfer from the LH wing fuel tank to the center fuel tank. This required that the aircraft be removed from passenger service and repaired prior to further commercial operations. The transfer had occurred overnight. The aircraft had been on the ground for approximately 16 hours and 2500 pounds of fuel had migrated from the left to the center tank. We were asked if we would be willing to ferry the aircraft. Seeing no major issue with the short flight; we agreed. The fuel was transferred out of the center tank and the fuel load rebalanced. It seems that when the fuel was transferred from the center tank; it was all put into the right tank causing a 3000 pound imbalance. We talked with Maintenance Control about the ferry permit and required paperwork to accomplish the short flight. The mistake that I made at this point was talking with Maintenance Control only; and not also having Dispatch on the line. As we pushed away from the gate; an ACARS printed message was received; indicating that our Maintenance Ferry Document was no longer current. It seems that even though Maintenance Control had assured me that we were legal and had all the paperwork correct; Dispatch was not completely in agreement. With truckloads of changes being thrown at us over the last month; it seems that the FOM and the maintenance procedures and definitions for a ferry do not line up or even use the same terms. After returning to the gate; we were able to rectify the difference in the manuals; and the ferry was safely accomplished. Even though we all know that Dispatch is our best resource in any situation; it is still so easy to work directly with our maintenance professionals as we did for so many years.