Rust help please.

Hello i am having this issue that i did not have before where everytime i try to alt-tab
my game just like seems to be crashing it takes soo long to get to the desktop and back into the game
and there is like a little stop sign on the bottom right corner of the screeen, please help!!

[editline]20th December 2013[/editline]

BUMP, i really need help with this please and a little update it isnt a stop sign it is a refresh sign with a red slash in it