I just purchased the Stack add on today, after i tried to create a post using the prebuilt single post page, my site returns a white screen. I contacted my server host support and they said the stack plugin is having an issue so they deleted it and the website is ok.
After which i tested further, if the YARPP plugin and Stack plugin is both activated the website is down. If I deactivate any of them then its ok. so i guess there might be a conflict between the 2.
Hope to hear from you soon. Thank you.