Why don't you download all skins available and try to reinstall them?
Maybe if you download the skins again and double-click (execute/load) them the Registry will be corrected and updated. Link here
For a technical solution try this, click start/then run & type in this regsvr32 actskin4.ocx (you might have to browse to the file in windows\system folder). This will reregister the Avast skin file & you should be able to run it.
A similar trouble was solved in this forum
For avast4.ini configuration, you can find more information here
. Although, I think it won´t be necessary.