If you are using .NET 3.5 hosting under medium trust then you need to copy the theme.skin file from the skin folder into /App_Themes/default folder, as there are known issues in that hosting environment.
When I test artisteer30-verticalmenu3 on my local machine it works fine, so other than the above I have no idea. If you fail to resolve it, you can zip your skin and email to joe [at] mojoportal dot com and I will see if I get the same problem or not. But first you should test the latest un-modified version of artisteer30-verticalmenu3 and see if it works or not. If it works then you must have missed some step in updating your skin.