Problem description:

IncrediBuild tries to distribute the tasks to remote machines but some (or all) remote tasks are canceled and executed locally.
Under the build monitor "Messages" tab the foollowing message can be seen:

Automatic Recovery XX:XX:XX (+X:XX) Local CPU X This task was re-executed locally by IncrediBuild as part of the OnlyFailLocally feature as it returned a non-zero exit code when executed remotely...

Possible reason:

This automatic recovery is part of V9.41 and instead of failing the build once the return code is not zero (on the remote machine) IncrediBuild tries to run the task locally. The reason for that is the problem may be related to our virtualization mechanism so when it will be rerun locally it will most likely succeed (unless this is a real failure).
It is possible to disable this feature (Agent Settings -> Initiator -> Advanced. Under the recovery section, uncheck the "Distributed tasks should only fail on local machine" option.
Once disabled, the tasks will fail remotely and the build will stop.

Solution:

If there are only few recoveries, it is ok to ignore them since the build should finish successfully once those tasks will be rerun automatically on the local machine.
If there are many recovered tasks, it is best to contact support so we can analyze the cause of those recovery attempts.