I had that problem with the 6.2 version when I was burying stalls and thrill rides. It would occasionally kick me out of the game (sometimes with less than 30 rides in the park). I discovered that I could use the 4.2 version and keep on working with no problem. It seems to be a random thing, because I have also used the ride tools with no problems in parks with over 100 rides/attractions. Sometimes after I use the 4.2 version, the next time I try with the 6.2 version the problem will have disappeared. Just be sure to save your game often, and under more than one name just in case something weird happens.