CL_ParsePacketEntities is an error that occurs because you are using a CD CRACK (or you patched your EXE with some kind of crack or trainer that was not made by Raven software).
Likewise a warez version of the game (which is most certainly using a cracked or hacked exe of some kind) will give this error.
Delete all your CD cracks and use only a legit copy of the game patched with the official 1.01 patch and join servers that are using the legit version of the game. The original disc or a 1:1 clone of disc one should be IN the drive when you play. If you still have problems substitute the actual disc 1 for the clone.
This should solve 99% of problems people have been reporting.
Invalid Game Folder means one or both of you have an illegal version of the game. Try another server is the best advice we can give.