Why you not download minerd(for CPU) or cgminer (Ati GPU) or cudaminer (Nvidia GPU) miner? If you need help to configure them just ask. The error what you see it with the python that is included to GUIminer "os" is a main package.
definitely not CEX.io - you will never see a return on BTC there Have a look on the likes of btc.jam, but there have been a series of scammers borrowing BTC there and defaulting.
On BTCJam should I only invest to A or B score peoples?
I just thinking of investing my btc into something. Where are you guys investing your coin? Is it worth to invest in mining at cex.io or any other site?