Response.TransmitFile virtual directory?

I can use Response.TransmitFile on my p.c. using VS2008  fine. But when I moved my code over to the server it won't work. Does the path have to be a virtual directory?
 
Lets assume you have 1 serverA with dir D:\ExcelReports and another serverB thats the webserver. So to transfer a file you would need something like Response.TransmitFile(D:\ExcelReports) ?
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