You need to run build with JDK or have tools.jar on the classpath.
If this occures during eclipse build make sure you run eclipse under JDK as well
(com.mysema.maven:apt-maven-plugin:1.0.6:process:default:generate-sources)

//
Try setting this to your eclipse.ini file and restarting eclipse to make sure that it's also using your JDK:
-vm
C:\jdk1.7\bin\javaw.exe

Cautions:

this must go just above -vmargs
you're full path to your VM maybe different than the one above
See this as reference.