I'm experiencing a weird problem on StackPrinter hosted on Google App Engine.
It seems that the application can't reach several endpoints; Stack Overflow and other endpoints still works.

This WORK (Stack Overflow)
http://www.stackprinter.com/export?question=478760&format=HTML&service=stackoverflow&linktohome=false

This DOES NOT WORK (Super User)
http://www.stackprinter.com/export?question=52483&format=HTML&service=superuser&linktohome=false

WORKING sites list:
Stack Overflow
English
Meta Stack Overflow
Programmers
Ubuntu
CSTheory
Webmasters
Photography
OnStartups
Statistical
Wordpress
Phisics
Role Playing Tex
Homebrew
Unix

NOT WORKING sites list:
Gaming
Apple
Super User Server Fault
Stack Apps
Web Applications
Ui
Android
Electronics and Robots
Mathematics
Cooking
GIS

Any hints?
@Kevin, could you please verify if StackPrinter's calls reach SE server?
This can be easily tested on Top Printed page.