PhysX is a real-time physics engine for adding realism to the game (see the end of the review ) and if you get the error message the first thing to doubt is video card driver update. Most probably your card don’t even offer the PhysX feature to the system.
So let’s take these simple steps to update the card first. For that go this is web page -- http://www.nvidia.com/Download/Scan.aspx (Supported browsers: Internet Explorer, Firefox & Netscape). In this webpage Nvidia will scan your computer and check your video card then offer the correct update for your driver. Once you downloaded the update and install it, the problem will be solved after rebooting the computer.
If it still not resolved the problem, check if the right video card is selected. It’s simple, go to the desktop right click and select Nvidia control panel – on the left side select 3D settings – Click on Set PhysX configuration - Click on the drop down menu to select your correct PhysX card.
If the problem persists consider this as the last resort, first make sure you have the latest video card update, If it still not working you need to remove Nvidia driver, go to http://www.phyxion.net/item/driver-sweeper.html and remove every bit of Nvidia including display and PhysX (NOT the chipset), then run the game. When it asks to install PhysX, do it from the latest video card update from the Nvidia or ATi site.
Why PhysX Necessary ?
PhysX is s a realtime physics engine which adds an element of realism in gamimg like weather effects, reactive debris, like weapon and projectile debris, realistic water and smoke effects, lifelike character, and every visual feast you are enjoying might have a touch of PhysX. In additon to that it is also a multi-headed physics simulation, has real time physics features like ragdoll effects, vehicle dynamics and volumetric fluid simulation and cloth simulation including tearing and pressurized cloth (Mafia II was the first to use this feature). So the modern games PhysX is going to be an essential part.
Hope this guide was useful, please vote. You can mail me anytime if you still have any comments, questions or suggestions.