If you downloaded the CS Retail 126.96.36.199 to 188.8.131.52 Upgrade patch -- you've probably run into some missing / wrong files (notably de_inferno and the de_survivor files). We'll post updated installers for those who haven't upgraded yet later this week or next. In the meantime, for those who already installed the Retail Upgrade, you can download the following 2meg fix. Extract the zip to your counter-strikecstrike folder:
CS Retail Upgrade Patch Fix Mirrors
And for those who are new to CS and the update patch system -- I encourage you to visit the new CS Download Wizard. It will guide you through the somewhat involved CS patch process to bring you up to date.
News source: Counter-Strike website