You would have to provide a full list of the effects and how they are used, what your comp and render settings are and a million other things. Could be a GPU driven effect like Element 3D or something, but we realyl can't know. Even some effects/ features that already come with AE can yield this behavior when used in specific combinations...
So, as I understand, AE don't provide information to determine what exactly prevents AE from multiprocessing render?
There is only this ambiguous message about "some" incomaptibility, which in fact tells nothing.
Hmmm, OK, so if anyone wants similar, more detailed info about what exactly is incompatible please go as me to https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform&product=12 - maybe if more people request this, maybe this information will be implemented in some future version of AE.
even if I solo only 2-3 layers without effects there is still "incompatibility" message.
default Classic 3D renderer of course.
so if soloing layers hasn't influence on this behaviour then the only way is delete layers/items one by one to derermine which blocks multiprocessing, but now I work on a 340MB someone's else AEP project with over 11.000 items in Project window, so it would be impossible to do before end of 2015.
There is a lost and explanation in After Effects Help:
See the "When After Effects temporarily disables multiprocessing with Render Multiple Frames Simultaneously" section.
In fact I read this twice before asking.
I would try to optimize my project by an example replace non-multiprocessing effects like Lens Blur with ordinary Gausian blur, but... in current version of AE there is no possibility to determine what blocks MP render and what exactly should be optimized/replaced.
Especially in project with 11.000+ footage and precomps.
Anyway thanks for a link, maybe someone will find it helpful.