Error compiling ptx file : "SM version assumed by .target is higher than SM version assumed"

I am trying to compile a ptx file with -arch-sm_20 (since i need the ld.global.cg instruction) but I get the “SM version assumed by .target is higher than sm version specified”. I am using the GPGPU-Sim pre-installed virtual machine (ubuntu 14.04, CUDA 4.2). Any help will be appreciated. Thank you.