Need Help working VirtualDub on Avast

I recently bought a refurbished computer, Windows 7 Home Edition (my old computer with XP died). I never had trouble editing videos with VirtualDub on my old computer Windows XP.
However, with the newer computer Windows 7 Home Edition, it won’t let me edit video files in VirtualDub.
I am using VirtualDub 1.9.11
When I try to open the video file, the following message pops up:
VirtualDub error:
Couldn’t locate decompressor for format ‘H264’ (unknown)

I tried opening another video file and got different message:
VirtualDub Error:
VirtualDub requires a Video for Windows (VFW) compatible
codec to decompress video. DirectShow codecs, such as
those used by Windows Media Player, are not suitable.

Can you help me?

Why do you think this is avast related?
Why do you post this in the viruses and worms forum section?

Download and install the missing codec.
Problem solved.

http://www.videolan.org/developers/x264.html

Thank you all for your replies.