When you setup a slave to do a build the tasks plugin fails to run with a NPE
(ignore the line numbers, they are off since the plugin has been modified a
number of times in CVS since the last release, I'll give the correct line
numbers later):

BUILD SUCCESSFUL
Total time: 7 minutes 13 seconds
Scanning workspace files for tasks...
FATAL: null
java.lang.NullPointerException
at hudson.plugins.tasks.WorkspaceScanner.invoke(WorkspaceScanner.java:63)
at hudson.plugins.tasks.WorkspaceScanner.invoke(WorkspaceScanner.java:23)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:1084)
at hudson.remoting.UserRequest.perform(UserRequest.java:69)
at hudson.remoting.UserRequest.perform(UserRequest.java:23)
at hudson.remoting.Request$2.run(Request.java:200)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:417)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:269)
at java.util.concurrent.FutureTask.run(FutureTask.java:123)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
at java.lang.Thread.run(Thread.java:595)

I've found what was causing the NPE issue and have 2 possible solutions
for it.

=====
Cause
=====

The NPE was happening on line 87 in WorkspaceScanner:

http://fisheye5.cenqua.com/browse/hudson/hudson/plugins/tasks/src/main/java/hudson/plugins/tasks/parser/WorkspaceScanner.java?r=1.4

87: Collection<Task> tasks = taskScanner.scan(new
FilePath(originalFile).read());

After debugging it turns out its because the taskScanner object is null!
The reason is because taskScanner is defined as a transient object:

32: @SuppressWarnings("Se")
33: private final transient TaskScanner taskScanner;

Therefore the object does not get serialized when the WorkspaceScanner
object is passed over the network to the slave.

==========
Solution 1
==========

Make the taskScanner non-transient. I like this solution as it is
simple, and the taskScanner should be passed along with the
WorkspaceScanner object I think. I may be wrong of course, we would have
to consult with the author of the plugin who is currently on vacation I
think.

==========
Solution 2
==========

Instantiate the taskScanner object at the point it is needed, not in the
constructor. This would of course mean the taskScanner member should not
be final - or it need not be a member at all, it can be a functional
variable. On the flip side we would have to make high, normal & low as
member variables.

After some discussion with Kohsuke I'll go ahead and implement solution 2. I
emailed you Drulli but it looks like you're on vacation, hope to touch base with
you when you're back to discuss/go over the changes.