btb bobs track builder flickering

Please I need Help with This Error "Can't export Object reference not set to an instance of an object" Someone Canm HELP ME to SOLUTION PLEASE??

Hi guys I'm sure it's rare to find a BTB noob in 2016 but here I am. Only my 2nd serious attempt at a design and everything is progressing nicely then suddenly, after exporting the track for a test drive, all the textures on walls, barriers, trees etc. are flickering and clipping through each...