Network share refuses to map.

I’m using a VB loginscript to set up XP clients on an Win SBS 2003 server. A section of the script maps shared drives. All the drives map OK except for one drive which is a users folder on a NAS server so the share path is \\servername\home$\%username%. This simply does not appear in My Computer, there are no errors, it simply doesn’t appear. If I change the mapping to \\servername\home$ then it maps fine so it’s to do with the username parameter somehow but I don’t know what.

Strangely another part of the script sets up desktop shortcuts, one of which links to \\servername\home$\%username% and this link works absolutely fine.

Does anyone know why the mapping using username doesn’t work? How can I get it to work?

Thanks for your help.