The community is also a great place to check out. Try these places for help from other users:
Please review the Third-Party Game Support topic to determine whether your question should be directed to the game developer or to Steam Support. Sending a support request to the wrong party may result in a delay in processing your request.
Retail CD-Keys for this game cannot be registered through Steam. If you wish to create a shortcut to this game under the Library tab, instructions can be found here:
This error has been reported as linked to the ASUS Xonar HDAV 1.3 Audio Device. Many users have found that disabling GX will resolve the error:
If you're encountering issues when launching or playing Plants vs. Zombies, make sure everything installed correctly.