White screen is ok for articlebot.php, in fact is a good sign that main settings are ok.
It's always good to confirm if your feed is ok with a feed reader (I use
www.bloglines.com).
I was not getting any post into my forums and I did this: Put the interval to 1 minute and the number of entries to be retrieved at 50 (I had like 28 entries in my blog but I read that articlepost.php can detect if there is less entries than you enter).
I run articlebot.php manually, got the white screen and after a few minutes my posts started to appear. You can refresh the bots manager page in your admincp and you will see when the next update will be.
After getting my blog entries I configured articlebot to 120 minutes interval and getting posts 1 by 1 again.
I hope it helps.