Some Crash when I play in Multiplayer and a lot of stuff is going on

When I play a game using a lot of resources happening at once it crashes. I thought it was something to do with the server so I checked in with them and they told me to tell you because it was something about the client. The only thing I did different since then was change my java from 32bit to 64bit. I hope you can help me with this problem. Thanks for reading!