Problem printing multiple duplex copies on a Brother HL-5370DW

[Pete]

I can no longer print multiple duplex copies on my Brother HL-5730DW. I can print single duplex or multiple non-duplex. I checked the settings and they do not seem to have changed, and I downloaded the latest driver, but so far no luck.

My system is:

OS Version: Microsoft Windows 7 Professional, Service Pack 1, 32 bit
Processor: Intel(R) Core(TM)2 Quad CPU Q8400 @ 2.66GHz, x64 Family 6 Model 23 Stepping 10
Processor Count: 4
RAM: 3070 Mb
Graphics Card: Ai Squared Mirror Driver, 3 Mb
Hard Drives: C: Total - 464684 MB, Free - 125480 MB; F: Total - 1907726 MB, Free - 1907317 MB; H: Total - 715227 MB, Free - 197619 MB; J: Total - 953634 MB, Free - 197036 MB; M: Total - 1907726 MB, Free - 612282 MB;
Motherboard: Dell Inc., 07N90W
Antivirus: Norton 360, Updated and Enabled

Thanks!

Pete