When you mapped the drives did you log back on with the same account? The drives are mapped PER user. So if you logon as Matt and map drives then shut down or reboot and then logon on as MattC the drives will NOT be mapped. You would have to map them for the MattC account, and then when you logon as Matt or MattC they will be mapped.
If that is not the problem let me know.
My Computer
At a glance
Windows 7 Enterprise (x64); Windows Server 20...16GB
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Dell OP7010
OS
Windows 7 Enterprise (x64); Windows Server 2008 R2 (x64)