I am so happy to have found this old thread. All of my almost 16 years in SL, this is the first time I have ever had this issue. I was in panic mode as this is a new laptop and I was worried that all of a sudden something was very wrong with my graphics card. After spending over a hour checking everything on my system and checking for updates, I logged back in to find still the same problem. Then I found this thread, I clicked everything with the issue to blending, then back to Alpha masking and noticed the mask cutoff was zero, set it all back to 100 and all fixed. Also this happened after the rolling restarts. I know it is old, but seriously thanks for this thread guys.