problem mapping drive by right clicking on my Computer.

I am using Winbuilder-078 and making a VistPE cd on a vista pc. Everything seems to work except being able to right click on the "My Computer" icon on the desktop fo the VistaPE cd and map a drive that requires a name and password. It pops up the window where you input the name and password, but then pops up another window that says "The mapped network drive could not be created because the following error has occured: A specific logon session does not exist. It may already have been terminated.".
I can click on the connect using another name and input the same name and password and it works fine. Is there something i am missing or doing wrong?