installation error

When I tried to install avast antivirus free I got the following error:
Return code: 0x2000000B [Invalid file signature. Setup will terminate]
Can you please help.
The problem is with my computer, not with the anti-virus program but I can’t seem to figure out exactly what it is.

any other security programs installed?
did you remove your previous used AV before installing avast?
did you run the vendors removal tool to clear all leftover files that may conflict?

tools http://singularlabs.com/uninstallers/security-software/

I did as you suggested. Still getting an error (a different one I think).

The avast log.txt is attached.

Thanks,