Solution: Failure accessing shares over VPN
Yes this has been a bug in Windows Vista. Its not possible to access shares via system running windows vista if NetBT is disabled. This issue has been fixed with a new hotfix KB933468. You can Google out "SMB (port 445) does not bind on Vista over RAS connection ".
It describes the issue in detail, just try installing hotfix KB933468 and your issue will be resolved. If not, then you can contact Microsoft support and address them your issue in detail. They are already aware of this issue and might suggest you other alternate solution for fixing the issue.