precomputed visibility needs to be rebuilt

[zeffo]

wat?

What does it mean and how can I fix this? Thanks in advance.

 

[Solestia]

Right click the game in your steam Library under detail view, click on properties then look for a tab named "LOCAL FILES". Click that tab, then click on the button labelled "VERIFY INTEGRITY OF GAME CACHE..."

It might fix your problem. Did you open a map in the SDK? Did you let KF2 run those initial things when you opened the game for the first time?