Is this the first time you have installed avast or has the skinning previously worked ?
I'm not sure what the module can't be found means as I don't have any ACTSKIN4.OCT on my system so it must be something that is created in the process.
Try a repair of avast. Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow. You need to be on-line to do this. I'm not sure how effective this might be as the skinning functionality is provided by a third party tool.
If that doesn't work try, uninstall, reboot, install, reboot. Ensure you have your Pro license key that was emailed before you reinstall. If this is the pro trial version, uninstalling will effectively end the trial and when you reinstall you will only have 6 days trial left (anti-piracy, etc.) so don't rush into this reinstall.
For some reason, ActiveSkin (the 3rd party library avast uses for skinning) does not seem to be working on your system. As a workaround, we may disable skinning in avast - that should solve the problem. Program Settings, Common, and uncheck any option with skins mentioned (see image, avast-no-skin).
If you are unable to access the above you can do this manually. To do that, open the file <avast>\data\avast4.ini, look up the [UserInterface] section, and add the following entry: StartWithSkin=0
