Error occurred during initialization of VM

build:
    [javac] C:\opt\Sterling\properties\entityDeployer.xml:759: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds
    [javac] Compiling 789 source files to C:\opt\Sterling\repository\entitybuild\classes
    [javac] Error occurred during initialization of VM
    [javac] Could not reserve enough space for object heap
C:\opt\Sterling\properties\entityDeployer.xml:759: Compile failed; see the compiler error output for details.
at org.apache.tools.ant.taskdefs.Javac.compile(Javac.java:1113)
at org.apache.tools.ant.taskdefs.Javac.execute(Javac.java:906)
at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291)
at sun.reflect.GeneratedMethodAccessor8.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
at org.apache.tools.ant.Task.perform(Task.java:348)
at org.apache.tools.ant.Target.execute(Target.java:390)
at org.apache.tools.ant.Target.performTasks(Target.java:411)
at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1397)
at org.apache.tools.ant.Project.executeTarget(Project.java:1366)