Understanding fsync error

Hi,

I'm getting more and more errors in the postgres log along the lines of :

2006-06-26 14:53:40 LOG: could not fsync segment 0 of relation 1663/16672/50807554: Permission denied
2006-06-26 14:53:40 ERROR: storage sync failed on magnetic disk: Permission denied

I'm pretty sure that I don't have any anti-virus, or other software running that could cause a file lock. The errors sometimes stop after a few minutes by themselves, but sometimes continue for hours - then stop when postgres is bounced. Theres more detail on this here http://groups.google.com/group/pgsql.general/browse_thread/thread/136494356086c702/ceaa221943c224b4?q=Steven+Ridgway&rnum=1#ceaa221943c224b4

Maybe I could understand this better if I could trace the error back to a specific table/index etc. When I get the error eg "... relation 1663/16672/50807554" I can see a file under the postgres data area whos name is the last number - but how do I trace whats in that file? Is there some way of doing this using system tables or something else? And what do the first two numbers in the error represent?

Many thanks for any light anyone can shed on this.

- Barry