DATA_ERROR with simple XML (long running task)

The following simple XML gives the error “DATA_ERROR Increase duration of parent task (2) or reduce EST of child task (3) or reduce duration of child task(3)”:

task1 2010,5,19 4336 0 task2 2011,11,7 40 0

From my point of view both tasks end the same day so that no error should occur. What’s wrong?