If you've done much troubleshooting of SoftGrid/App-V virtual applications then Process Monitor is probably one of your most highly valued tools. It'll quickly and easily tell you what's being accessed, who's doing the accessing, and is a quick way to determine if your problem is rights/permissions related as well. I've posted on Process Monitor multiple times in the past so I won't go into all the details about the greatness of this tool other than to say there's a new version available.
You can download Process Monitor 2.0 here.
J.C. Hornbeck | Manageability Knowledge Engineer