This ahppened most likely because the Bolt was not properly slid all the way back or it slide forward when you where aiming. If the bolt is not in place properly the dry fire preventer pin will drop and catch the string when fired. When you push the bolt all the way back into place the pushs the dry fire preventer arm up into the assembly disabling it. Also make sure you are useing either there omni-nock or a flat nock. The company has told me all the xbows will work with both, but the do not recommend the use of half-moon nocks as it can cause problems with the dry ire preventer.