Unable to create qcow2: Invalid image size specified!

Hello all,
I am trying to create a qcow2 using

" # qemu-img create qcow2 windows.qcow2 8G "

This commands results in this error :

" qemu-img: Invalid image size specified! You may use k, M, G or T suffixes for
qemu-img: kilobytes, megabytes, gigabytes and terabytes"

I have tryed k,m,g,t upper and lower case all this the same result. Also tried different sizes. I have used this exact command before and it worked fine. This is a fresh install of ubuntu 12.04 LTS.

Thanks!