I have a PogoPlug Biz.

I have another user setup to see a folder on the Biz.

This user logs in, and collaborates a folder to me as 'User' permissions.

I log in as myself on my iPad, view PDF's perfectly.

I log in as the user on their iPad, they tap the PDF and it will not open. 

When trying to open in DocstoGo or Adobe Reader on the iPad, it says the file size is zero.

Once again, I log on as myself, and it works perfectly. 

Hardware: iPad II with latest OS. 

Another test: I also have an iPad I with the latest OS, and log on as the user, it works perfectly fine. So it only seems to be an issue with the collaborator on the iPad II.