Fail in virtualization of an Acronis backup

Hi,
I have a problem when trying to virtualize a previously created Acronis backup under Windows 7 Home Premium.
I did a complete Acronis backup and then:
1 - I converted the .tib file in a .vhd file with Acronis and then I tried to load it as a virtual machine in VirtualBox.
It fails due to an "installation os disk missing": Windows cannot starts and requires the installation disk

2 - I created the .tib file and I tried to load it with VM Player 3.0 (it supports .tib files): it fails with a "strange error"

Is there any particular option that I have to set when backing up the system ?
Can you help me ?
Thanks
Best regards
Daniele