PANIC: cannot abort transaction 140578842, it was already committed

Hi, all.

any idea about causes and consequences?

C:\>psql -U postgres monitor
Welcome to psql 8.2.4, the PostgreSQL interactive terminal.

Type: \copyright for distribution terms
\h for help with SQL commands
\? for help with psql commands
\g or terminate with semicolon to execute query
\q to quit

Warning: Console code page (850) differs from Windows code page (1252)
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page "Notes for Windows users" for details.

monitor=# vacuum full
monitor-# ;
ERROR: could not truncate relation 18293/18295/19113 to 68908 blocks:
Permission denied
PANIC: cannot abort transaction 140578842, it was already committed
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>

Att.,
Sergio