It states the following..
If you're using the SDK 2013, add the following definition to a $PreprocessorDefinitions variable in your client VPC project: SOURCE_2013. The default projects already have this variable in their $Compiler blocks. Add the new definition at the end, after a semicolon.
https://developer.valvesoftware.com/wik ... stallation
Ok so ive found the $Compile block in the client_base.vpc (Im assuming thats the correct one), what is it telling me i have to add?