memory cannot be written seems like there is an issue with tf2 not being able to write in the memory anymore. Is there still enough room on your hard disk where steam is on? If there is enough try elevating your virtual memory a bit and see if that makes a difference, maybe that is the problem although it should specify that it's virtual memory. Did you do anything (think settings and memory) since the last time the game had no problems? is it read or written? try running it all as administrator.