Forgot to mention, even in the conditional styles I added to my header, IE still cannot parse background images… bizarre. I’m having some other issues with BuddyPress (does not appear in plugins list), so maybe they are related.
By the way, I notice that in the default adminbar.css, the div #wp-admin-bar has three different z-indexes: 99, 999, and 1000 (#wp-admin-bar *). I am no z-index wizard, but that seems odd to me. That 99 seems wrong.
I had this same issue. Check your error logs to see if it is a memory issue. My hosting provider changed my PHP limit from 32 to 64 and that solved the blank page problem (or so it appeared). However, even though the page now displays, I still have an issue with the forums not working correctly so maybe this doesn’t help at all.
I’m also having issues with the bbPress forum installation. Upon installation, the Forums navigation tab appears, but when clicked leads to a blank page. I have tried reinstalling several times. This is a brand spanking new installation of WPMU and BP.
