The patch 3.4 makes it possible to install mods developed with REDkit. If you wish to install the patch 3.4 find it here. Please note that 3.4 requires Enhanced Edition + 3.1, 3.2 and 3.3.
In the patch 2.1 Microsoft’s .NET Framework 4 became necessary to run The Witcher 2, which fixed several problems with game-to-server communication. However, in some cases this also led to problems with launching the game, notably to errors like “application was unable to start correctly (0xc0000142)” and similar, which most often resulted from conflicts between .NET 4 and other applications.
THE DOTNET HOTFIX
We created a hotfix especially for the people who experience the problems mentioned above. The hotfix makes .NET Framework 4 unnecessary to run the game. The hotfix will work correctly ONLY when applied on the game updated to 3.4.
PLEASE NOTE! This hotfix SHOULD NOT be used with the Steam version of the game. A solution for the .NET 4 problems for Steam version users was included in the 3.1 patch.
If you would prefer to not use the hotfix then the following suggestions may potentially prove helpful:
REINSTALLING AND FIXING .NET FRAMEWORK 4
Keeping your Windows fully updated is advisable. Additionally, for potentially broken .NET Framework installations Microsoft recommends Microsoft .NET Framework Repair Tool to be found HERE.
KNOWN CONFLICTS WITH EXTERNAL APPLICATIONS
There are several known instances of external applications conflicting with .NET Framework 4 in this context:
SYNCHRONISING THE INTERNET TIME
In some cases synchronizing the internet time on Windows was of help. However, this option is available only on some setups. When it is it can be found in Control Panel\Date and Time as an additional tab Internet Time. To adjust it use the Change Settings box available in that tab and select Update Now.
Additionally, starting the game after performing a clean boot on your computer might help in determining whether an external application prevents The Witcher 2 from launching correctly. See how to perform a clean boot in Windows XP, a clean boot in Windows Vista/Windows 7.