It has nothing to do with how many dimensions there are in a model.
It has everything to do with how many dimensions are in a model site, how many models are in a model site, and how many member sets are in a dimension. It seems that if you add all dimensions, all hierarchies, and all models in a model site they cannot exceed 128 or else you get this error.
The staging database contains a table which can assist to ensure that these limits aren't exceeded.
select * from fk_relationships where scope =