Vacuum Failed - backend closed the channel unexpectedly

Running Linux 2.2.14 postgresql 7.0.3
I am trying to run a vacuum and I get the following output

vacuum;
NOTICE: FlushRelationBuffers(menudt, 6): block 3 is referenced (private
0, global 2)
FATAL 1: VACUUM (vc_vacheap): FlushRelationBuffers returned -2
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.

This is only a test database so I can blow away the table and rebuild it
but if this is not a known problem then I could do some debugging.

Dave