This is the most common technical cause. The GoldSrc engine was built in an era where 512MB of RAM was a lot. By default, the engine has a heap size limit. If your portable version includes high-definition models (common in "HD" portable builds), the engine tries to load too much data into its limited memory buffer and crashes.
Portable versions of games are essentially cracked, pre-configured directories. They are convenient, but they are also messy. Here are the three main reasons portable CS 1.6 builds crash during precaching: cs 16 precaching resources problem portable
The error often points to specific models. Because you are portable, you likely lack standard weapon models. Download a clean models folder from a trusted archive and copy these files into cstrike\models\ : This is the most common technical cause