standalone runtime errors?

ok so ive recently packeged a game into a standalone .exe. but when i try to run the game i get an error saying “This application has failed to start because pthreadVC2.dll was not found. Re-installing the application may fix this problem.” but when i go to the folder that has the exe in it, all of the files are there, including “pthreadVC2.dll” so why is this error coming up if it never did before?