VH-JCH was cleared by Albury Tower on the direct track from Albury to Canberra at 9000 feet. VH-CSV was on the same track flying from Canberra to Albury and believed (by Albury Tower) to be at 8000 feet. Accordingly, the pilot of VH-JCH was given a requirement to reach 9000 feet in time to avoid a conflict. This was complied with. The pilot of VH-CSV called Albury Tower at 45 miles from Albury (10 miles prior to controlled airspace) and was cleared to Albury and to descend to 7100 feet which is the applicable route lowest safe altitude. VH-CSV then reported leaving 9000 feet. This was the first the Albury Tower controller knew that VH-CSV was at 9000 feet. The pilot was instructed to descend immediately to 8000 feet. This altitude change was probably achieved before the aircraft entered the control area and hence a loss of separation, technically, probably did not occurr. VH-CSV had originally maintained an 8000 foot cruise altitude but had later climbed to 9000 feet and advised Melbourne Flight Service of this change. The flight service officer was the only person on duty for this area of the network and a busy complicated period of work was in progress. She attempted to contact Albury Tower to pass advice of the level change but was unable to get through. Albury Tower was also operating with one person on shift and was in a busy period. Uncontrolled airspace between Canberra and Albury btween 8000 feet and 10000 feet spans a track distance of only 39 miles. Aircraft of the type involved in this incident transit that distance in a fairly short period of time. Due to the workload imposed by other tasks at both Albury Tower and Melbourne Flight Service, the co-ordination on the altitude change for VH-CSV was not achieved, although every effort was made. Significant Factors The following factors were considered relevant to the development of the incident: 1. Operation of air traffic service positions by one person during busy traffic periods. 2. Co-ordination on altitude change for VH-CSV, by the flight service officer, was not achieved.