This is something I have been trying to figure out for months now.
I have multiple portals on one DNN installation.
In my skin.css file, the .MainMenu_SubMenu class has the entry:
filter:progid:DXImageTransform.Microsoft.Shadow(color='#696969', Direction=135, Strength=3);

This filter works for only 1 of the portals. There is no shadow shown on any of the other portals.
This is true even if I use the same skin for each portal.

I also have a photo gallery module that displays a slideshow. There are some filter functions in it as well.
document.images.SlideShow.style.filter="blendTrans(duration=2)";
document.images.SlideShow.style.filter="blendTrans(duration=crossFadeDuration)";
document.images.SlideShow.filters.blendTrans.Apply();

The slideshow works perfectly well on one portal but not on any of the others.

When I check the javascript error it just tells me there is an unspecified error: code 0.

The really strange thing about this is it only happens on the pc that I use for development.
I have re-installed the OS. This did not help either.

If anyone has run across something like this before, I sure would like to hear about it.