vacuumdb -a -z hangs

I have a cronjob that does a vacuumdb -a -z every night.
When i came to work this morning i saw a lot of postgres processes hanging
on wait.

The last thing i see before it hangs is this:

-------------------------------------------------------------
NOTICE:  --Relation pg_toast_1216--
NOTICE:  Pages 0: Changed 0, reaped 0, Empty 0, New 0; Tup 0: Vac 0,
Keep/VTL 0/0, Crash 0, UnUsed 0, MinLen 0, MaxLen 0; Re-using: Free/Avail.
Space 0/0; EndEmpty/Avail. Pages 0/0. CPU 0.00s/0.00u sec.
NOTICE:  Index pg_toast_1216_idx: Pages 1; Tuples 0. CPU 0.00s/0.00u sec.
NOTICE:  Analyzing...
-------------------------------------------------------------

is this a known problem?
Postgres is version 7.1.1.

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