If there is a program that is writing to log files, etc. then ashserv will do as it should scan created/modified files. So if this is happening at shut-down there is likely to be an error.
The trick is to find out what ashserv.exe is scanning, e.g. what other program is running. How you do that is a problem. A long time ago I kept getting a shut-down error written to the winXP event logs (I monitor this regularly), I never 100% found out why but installing a MS service uphclean.exe resolved it, no more errors on shut-down in the event logs.
Is this your solution, I really don't know.