robocopy slow when running in task scheduler in windows 2008 r2

Hi,

I'm testing robocopy (built-in command in win2008r2):
1. server A: win2003 (32-bit)
2. server B: win2008r2 (64-bit)
3. copy speed is ~480MB/min (running robocopy in command prompt directly)

Found that, when running the robocopy as scheduled job (configured in task scheduler), the average speed dropped from 480MB/min to 100MB/min. Please help and advise how to improve the speed when running as scheduled job.

Thanks.