Dynamips on linux

anabel8830

I need your help my problem is with dynamips you see I am working with a virtual machine on amazon ec2 with operating system ubuntu and always I try to run a net file I get this error:
Launching IOS image at 0x80008000... Error : compressed image checksum is incorrect 0x217BB7E4 Expected a checksum of 0xF05B4952 !!! WARNING - VM is not running, will be unresponsive (status=1) !!!
I do not know if the image is corrupted because I used SFTP to transfer the file from my pc to the virtual machine because everything is working fine on my pc with the same image. I have tried many things like changing the ios image and always the same. I would appreciate your help because I am running late for this project. THANKS in advance