Game crashed. When I successfully lowered the first platform after activating all 4 buttons in the beginning of the level (see image below), I placed my blue portal on the target in the distance, then my orange on my right to reach it before the timer ends and destroys my portal. The game crashed when I shot my orange portal. I think what may have happened is the timer ended exactly at that time and maybe destroyed my portal while it was being placed.

https://s4.postimg.org/y0xe8zpjh/Bug_TWTM-_Portal_Destroyed.png

I was able to complete the level without the crash after restarting the game and placing my portals when the timer still had a few seconds left.