To compile projects created with the Crosswalk SDK, you must set the CROSSWALKSDK_ROOT environment variable.
On Windows systems, you can open a command prompt with the required environment variable already set by choosing Start 
Programs Softimage Products Crosswalk vx.x Crosswalk Command Prompt.
You can also set this variable at any command prompt by manually running setenv.bat located in the <CrosswalkPath>\SDK folder. This batch file sets CROSSWALKSDK_ROOT.