backing up SD card data from two partitions

I have currently installed the latest xillinux OS on a 7020 Microzed Board. I used the USB image kit version 1.61 in windows 8 to install the OS. Images were downloaded from here (http://xillybus.com/xillinux). So there are two partitions basically created by this image, one boot partition (FAT 32) and another ext4 root fs partition.

There was no issues burning the image into the SD card and booting the system on microzed. But, after working on the system, writing code, configurations, etc, I wanted to take a backup of the entire SD card (both partitions). So, I tried to use the USB Image kit version 1.61 to create a backup image in the img.gz format. I was able to create this backup image. But, now when I mount this new backup image again in device mode using the USB image kit software on another SD card, the mounting takes for ever, and after like 10 minutes, there is an error generated with error code 0 saying that Could not access the USB device (Code:0).

I also tried to mount the image created using win32disk imager software. After the image is mounted, and I try to open the SD card, it says SD card needs to be formatted.

Can anyone suggest me how to backup a SD card completely (Both partitions) and mount it in a another SD card in windows . Which software would you recommend ? What is the best way of doing it ?