I took a contract to hunt them down and everytime just as the game is about to switch to the battle-screen it crashes with the following error-message:

A critical error occured:

Unable to open file
"sounds/enemies/dlc2/giant_spider_hurt_01.waw"

The program will now terminate.

Tried verifying game-files but that didn't help. Any suggestions?

Well, I solved it by going into settings and ticking the checkbox for the Beasts & Exploration DLC. (I had downloaded it manually rather than going trough the galaxy-downloader so it wasn't on the list)