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.