PostgreSQL hanging

I am runing PG 8.1.4/Windows.
Over the weekend, I have had to restart the PostgreSQL service a couple
of times after PG hangs.
At the time this happens, the log is showing entries such as the one
below

2006-07-31 09:19:55 LOG: could not rename file
"pg_xlog/0000000100000208000000E1" to
"pg_xlog/0000000100000208000000F4", continuing to try

Any ideas what may be causing this?

My database is currently 7.7 GB.
I have 54GB of drive space available, so it is not being caused by lack
of disk space.

My autovacuum parameters are as follows:

#-----------------------------------------------------------------------
----
# AUTOVACUUM PARAMETERS
#-----------------------------------------------------------------------
----

autovacuum = on # enable autovacuum subprocess?
autovacuum_naptime = 20 # time between autovacuum runs, in secs
autovacuum_vacuum_threshold = 100 # min # of tuple updates before
# vacuum
autovacuum_analyze_threshold = 100 # min # of tuple updates before
# analyze
autovacuum_vacuum_scale_factor = 0.1 # fraction of rel size before
# vacuum
autovacuum_analyze_scale_factor = 0.1 # fraction of rel size before
# analyze
autovacuum_vacuum_cost_delay = 100 # default vacuum cost delay for
# autovac, -1 means use
# vacuum_cost_delay
autovacuum_vacuum_cost_limit = 100 # default vacuum cost limit for
# autovac, -1 means use
# vacuum_cost_limit

Any suggestions will be appreciated.