BACK UP on External USB Harddisk

I am using a POWER EDGE T110 II with WINDOWS SMALL BUSINESS SERVER 2011 ESSENTIAL....  on DASHBOARD => COMPUTER and BACK UP => i want to back up my server on an external USB-harddisk with 1,5 TB.

C:/ is about capacity 197GB  (free about 125GB)

D:/ is 3,5TB Capacity (Free about 3 TB

I want to BACK UP  D:/  but Windows told me, that this is not possible because D:/ is larger than 2GB.

If tried to use a bigger External USB Hard Disk, but for the Back up the USB Hard disk should be smaller than 2GB.

What can I do to Back up ?

When I´ve set up my server and the Back up in 2013, it worked to back up on external USB Disk, but for some reasons, it does´t work any more.

has anybody an Idea ?