Error occurred please contact the application owner

Error occurred please contact the application owner

For some reason my form stopped working the other day I cannot figure it out for the life of me. I select a drop down and it just breaks. An error message pops up that says "Error occurred please contact the application owner" Is there any good way of debugging the issue? I've put alerts all over the code trying to figure out when exactly it breaks and I'm still not even sure I fully know where it is breaking. Any help would be appreciated.