Pronterface won't start printing (2 replies)

I'm new to reprap. I just finnished assembling my Prusa Mendel I2, and was able to get some prints. Sometimes I wasn't able to start a print but I was able to solve the problem by closing and re-opening pronterface. This time I'm not able to solve my problem. When I start the print this shows:
T:202.0 E:0 W:?
T:201.6 E:0 W:?
T:201.1 E:0 W:?
T:200.8 E:0 W:9
T:200.3 E:0 W:8
T:200.0 E:0 W:7
T:199.6 E:0 W:6
T:199.2 E:0 W:5
T:199.0 E:0 W:4
T:198.7 E:0 W:3
T:198.3 E:0 W:2
T:198.0 E:0 W:1
T:197.6 E:0 W:0
When W:0, print is supposed to start, but in this case it doesn't. What's wrong?