With the attached scene, that otherwise renders fine, if I enable Motion Blur, I get an error every few frames:
“particle_array.insert_particles() - Did not recieve the expected number: 1666669 of particles.
Instead it received: 1666667 particles.
The stream still has: 1 particles”
Mixamo generic T-Pose Krakatoa 03A.c4d.zip (1.14 MB)
Logged as bug, thank you!
We are still waiting for an X-Particles license though, so we cannot test this right now.
I can confirm this error. I’m using X-Particles 2.5 and get this message:
Doesn’t occur with motion blur off, and doesn’t seem to matter how many particles XP is emitting or max. particle count.
Running beta build no. 2 on OS X Mavericks, C4D R15.
I have a suspicion what is causing this, in fact there is a note in the source that warns about this situation, but I think the logical condition is not handling every possible case. But I will have to wait for our developers to come back from holidays to look at the code. Also, we still don’t have an X-Particles license to test this here, so we might have to wait for the X-Particles developers to come back from holidays, too 
I think we can actually solve this very simply. But like Bobo said, I can’t test the fix at the moment.
Thank you for reporting the problem!