Thank you for contacting The War Z customer support.
Unfortunately, as of the May 30th patch, the ATI Radeon HD 4800 Series graphic card does not meet the minimum system requirements:
OS:Windows Vista/Windows 7 (enhanced for 64-bit OS)
Processor:2.4 GHZ Quad Core or better
Memory:4 GB RAM
Graphics:Nvidia GTX 460/ATI Radeon HD 5850
Hard Drive:3 GB HD space
Sound:Windows Compatible Sound Card
Other Requirements:Broadband Internet connection
We apologize for any frustration or inconvenience this may have caused you, and we thank you for your continued patience and understanding.
After reviewing the file, we see that your graphics driver has not been updated since November 11th, 2012. We suggest navigating to AMD.com. You will find in on the right-hand side of the upper tool bar a 'Find a Driver' tab. From here, you can either manually select your graphics card, or have AMD software determine the appropriate update for you.
Be sure to check for updates on the forums at http://forums.playwarz.com/index.php?/forum/7-patch-notes/
If you have any additional questions, please feel free to submit a new ticket and we will get back to you as soon possible.
The War Z Customer Support