On Mac OS X you can see sometimes that a page in htmlviewer does not show. The HTMLViewer turns white. That's bad for batch processing if you need to do something on the webpage.
For my application I solved this by using ScreenshotWindowRectMBS in the DocumentComplete event. I get a picture form the control. Now I use pic.CountColorMBS(&cFFFFFF) to count the white pixels and if that number is more than 95% of width*height, I set a flag. This flag causes another part of the app to reload the same URL in the htmlviewer. This may not be a solution for everyone, but for me it works