Please Help

Hi. I am new to n64 emulation so my problem is probably becuase of my own stupidity but i need help. I just got pj64 yesterday, and I got mario 64, excite bike, and harvest moon 64. I have got mario to work fine once, But when I go to play it the second time at the bottom of the window it says loaded 25%, 50%, 100% then it says at the bottom SAVE STATE SLOT SUPER MARIO 64.PJ and soon as that appears i get an illegal opperation. The same thing happened with excite bike. But with harvest moon it didnt even work the one time. I have uninstalled and reinstalled and mario will work again. I would really appreciate it if anyone can help me figure this out. Thanks

where can i find out te specs you need? thanks