Flowizard - error, inverted elements?

cokedrinker

Hello,

Well im new to flowizard.. using it for a design project by analysing wind movement throughout a site consisting of skyscrapers. I've done an autocad model of a skyscraper on its own (no ground level, its in suspense)and played around with the program... all went well. However when i decided to add more detail to the cad model, ie the ground for more realistic results, . It gives up midway through the calculation. During the third stage of calculation, Mesh Regions, i get the following message - Unable to generate a valid computational mesh (due to inverted elements). Anyone know what the problem is and how i can rectify it? Any help would be much appreciated.

Cheers!