After I installed SUPEE-7405 on our CE 1.9.1 version on CentOS, Order was no longer visible to the Admin.
I would go to Sales>Orders>Select one of the orders. The order page would only show "Order View" and "Information" and empty page.
I removed SUPEE-7405 (PATCH_SUPEE-7405_CE_18.104.22.168_v1-2016-01-20-04-42-03) patch and our orders started to appear again.
Has this happened to anyone else? How can I still go ahead and install this patch?
It happens to everyone who is running the old, outdated and no longer supported php 5.3 and you have one of two choices,
A) the more PCI correct, quit running a version of php that is no longer getting security patches. There is a php 5.4 support patch available on the same page that you download the security patches from for 1.6.x.x through the 1.9 version previous to when php 5.4 support finally got slipstreamed into the Magento distribution and have your hosting provider upgrade your server to use php 5.4
B) keep running php 5.3, ignore any security issues doing this might cause and search the Magento 1.x security patch forum on this website for this issue as the php 5.3 code change has already been posted here in 2 or 3 of the threads.
This is present in Magento builds running PHP 5.5 as well - it is not limited to 5.3. We're tracking several customers complaining of the same post-patch.