Would you please post the information in the body of the message and provide your computer specs? People will be hesitant to open the attached file since you didn't provide much info and you have a recent join date (i.e. we don't know you and want to make sure you are not hurting our computers or kidnapping us).
Also, are you receiving an error any time you try to test a level or is the problem isolated to just one particular level? That is, if you start up a new level, put nothing in it, will it load when you test it? This is important for us to know in order to best help you.