I encountered a problem today trying to create an Apache Tomcat virtual directory that pointed to a mapped network drive.
Found out that this was due to the fact that Tomcat was running as a Service with a local account. It was not able to see the network drive since that used to get mapped with the logon scripts.
Solution was to either run Tomcat Service my account or run the startup script from the command line. Tried the command line option and it recognized the network drive.
This is probably true for any web server that runs as a service.