Crashing when grouped with a friend

Hello all,

When I play the game solo, there is no problem

When I group with a friend of mine, it used to be that the game would crash whenever I used a portal of any kind.

Today I ran a test, and it's crashing in the middle of a level, and not just when I use a portal.

I have used different characters, they have used different characters, and we have the same problem.

It also only seems to be me; they don't crash, but I do.

Please help.