Scheduling Two backup tasks at the same time

Hello.

I want to do a security copy of two folders from hdd E to hdd F and G. A créate two task for executing at 20:00

wbadmin start backup --backuptarget:F -include:E:\grpsp,E:\usu -vssFull -quiet

and

wbadmin start backup --backuptarget:G -include:E:\grpsp,E:\usu -vssFull -quiet

But it only execute one of them, because shows another task is executing.

How do i can solve this?