Windows Deployment Services "the specified image file is either invalid or corrupted"

I'm trying to add images to a virtual server running WS08 R2 but the only type of images that get accepted are the vista x86, nothing else works,
I tried the following image files:
windows server 2008 R2
windows server 2008 x64
windows 7 x64
windows 7 x86
windows vista x64

and always the same error: "the specified image file is either invalid or corrupted"

the machine configuration is as follows:
Virtual machine on Hyper-V 2 (host is WS08 R2 Enterprise)
2048 MB RAM
25 GB free diskspace

running these roles:
AD
DNS
DHCP
WDS

hope someone can help