EA Results disparity with demo/real

Hello,
pls can someone tell me why a particular expert advisor will perform very well on demo with a particular broker and when that same EA is used in the real account of that same broker, it performs poorly or even with losses? Pls, how can i fix this problem?

David

Demo orders are usually placed instantaneously. Real orders tend to lag.

and a lot of brokers have price feed differences from demo to live...it is covered up instantaneously hence actually trading both of them is the only accurate way to determine..as you have found out

Thank you very much for the replys, i appreciate it. But is there no way around this?