Dear Mark,
From your description I believe the Projects and Library (attachment) folders are located on an external drive (most likely connected via fiber optic cable). The problem is this external drive starts up after the BIM Server starts up. The BIM Server expects these folders to be available once it is on line. This odd mount point is created at this point.
You need to delay the start up of the BIM Server, to after the daemon that starts the external drive. I have been told (but I have not done this), that this delay can be done by moving the plist for the external drive daemon from the /System/Library/LauchDaemons folder to the /Library/launchDaemons folder. I would consult a MAC OS X systems expert first before trying this.
Ed
Graphisoft Technical Support