I am currently getting this error when i am importing the m2i to export it as m2. I am using the clockworkhorse as my base model:

EDIT: it would seem the problem is with the size of the file or the number of vertices. As i remember reading, there was a max number of vertices of roughly 6000 and my model has roughly that much vertices. I will update if i find a solution!
EDIT2: wow...i can't believe that this error occured to me before and i forgot about it. This is where phantomX solved the solution

Hello everyone.
Since I am new here I can't post links, so here is M2tool error text :
File: M2.cpp
Line: 2148

Expression: ( Elements[iElement].Offset <= AnimationBlock.oTimes ) && ( AnimationBlock.oTimes < ( Elements[iElement].Offset + Elements[iElement].DataSize ) )

As you can see it is exactly the same problem here when I am trying to increase vertex amount on CelestialHorse.M2 model and on any creature models which was released in cataclism or later. I tried to use 010 Editor like phantomX said and changed nParticleEmitters to 0  with ofsParticleEmitters to 0. After that m2tool converted my m2i to m2 without any errors, but in the game my model is fully invisible. Can someone tell me please how can I fix this issue? I want to import any WoD mount to blender, increase the vertex count on it and export to the game if it is real with existing m2mod redux 4.6.1.