Issue Regarding the Move from Demo to Real Time

Hello, 

 Thanks for reading this post.

 Currently, I am automating a trading strategy, and we have backtested the strategy, and have validated it by backtesting through other software and checking that the trades match up; however, even though the results in are backtesting are matching up, when we are looking at real time trades, they are not matching up with our other software as well. Specifically, we would run the model on our demo account for a few days and would print out a report with all of the trades that occured, and they did not match up with the backtester. I was wondering if anyone would know why this would occur. 

Thanks