The two primary reasons are either insufficient security given to the service or a security credential conflict that occurs when the logged in user attaches to a remote machine under a different user than that which the IPSentry service is running or configured to access the remote drive.

For example, if IPSentry is running under account USERA and is monitoring drive space located on \\COMPA and USERB logs into the desktop and maps a drive as USERB to \\COMPA you will end up with a session credential conflict.