There are 3 missions in the Protoss campaign in which you will loose from the start or you don't have a chance of winning (no matter how good you are at SC-BW)
These are (in campaign order): The hunt for Tassadar > Into the Darkness > Homeland !!
In this missions you don't stand a chance if you play fair (without using cheat codes).
Right from the start of the mission you'll loose (if you play fair:D). What i recommended in the first news post i will recommend again: God code until you clean a small area of enemys (to biuld your base) after which you dissable God code OR Skip Level Code.
That is all and Take Care !