error c3.cab

where i can get c3.cab

because my c3.cab is corrupt

I can't seem to find this file inside my BFBC2 Beta install directory within Steam's directory.

Try deleting it. Then once in Steam, right-click BFBC2 Beta > Properties > Local Files tab > Click the 'Verify integrity of game cache...' button.

Let it check for missing files. Hopefully this will resolve your issue.