NullPointer when starting build on slave

[AusJonny]

I have configured a Windows build machine as a slave on Jenkins and everything seems to be started fine but when kicking off the build for a project I just get this:

Triggering x.x.x.x
x.x.x.x completed with result FAILURE
Finished: FAILURE

digging deeper I find this exception:

Started by upstream project "myProject" build number 46
Building remotely on x.x.x.x in workspace c:\jenkins\workspace\myProject\label/x.x.x.x
hudson.util.IOException2: remote file operation failed: c:\jenkins\workspace\myProject\label/x.x.x.x at hudson.remoting.Channel@12bb213:x.x.x.x
        at hudson.FilePath.act(FilePath.java:828)
        at hudson.FilePath.act(FilePath.java:814)
        at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:743)
        at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:685)
        at hudson.model.AbstractProject.checkout(AbstractProject.java:1218)
        at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:581)
        at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:470)
        at hudson.model.Run.run(Run.java:1434)
        at hudson.matrix.MatrixRun.run(MatrixRun.java:146)
        at hudson.model.ResourceController.execute(ResourceController.java:88)
        at hudson.model.Executor.run(Executor.java:239)
Caused by: java.io.IOException: Remote call on x.x.x.x failed
        at hudson.remoting.Channel.call(Channel.java:655)
        at hudson.FilePath.act(FilePath.java:821)
        ... 10 more
Caused by: java.lang.Error: Failed to deserialize the Callable object.
        at hudson.remoting.UserRequest.perform(UserRequest.java:104)
        at hudson.remoting.UserRequest.perform(UserRequest.java:48)
        at hudson.remoting.Request$2.run(Request.java:287)
        at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
        at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
        at java.util.concurrent.FutureTask.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
        at hudson.remoting.RemoteClassLoader$ClassLoaderProxy.readFully(RemoteClassLoader.java:470)
        at hudson.remoting.RemoteClassLoader$ClassLoaderProxy.fetch2(RemoteClassLoader.java:418)
        at sun.reflect.GeneratedMethodAccessor97.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at hudson.remoting.RemoteInvocationHandler$RPCRequest.perform(RemoteInvocationHandler.java:274)
        at hudson.remoting.Request$2.run(Request.java:287)
        at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:619)
Recording test results
Finished: FAILURE


Any idea what could cause that?

Thanks

Jonas