Are you using P4 or P5? I had a problem with eye MAT poses in P5. I fixed it by loading an existing DAZ partial MAT into MPE and then changing the textures to mine and saving it out again. MPE does not support partial MAT poses for P5 if you're making them from new.

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"you are terrifying
and strange and beautiful
something not everyone knows how to love." - Warsan Shire