=IF(AND(ISBLANK(g4),ISBLANK(h4)),"",IF(AND(g4<800,h4<800),"M/R", IF(g4<800,"R", IF(h4<800,"M", ""))))
GOT IT!! It was correct it was not picking up the correct cell number. When I copied it it stayed as the first cells I pasted it into!!! thank you all so much!!!kpark91's worked with mine. Are you sure you've copied it down the column properly?
Usually the inconsistent message means the formula is different to the one below/above etc