I\'ve given an ad hoc version of my app to some users. Two of them have the app die on start up while one user has no issues. I can also install the ad hoc without issue...but
The key word I think you have used is the word 'dropbox'. I've just spent the last 2 weeks trying to work out my app would not work on other machines and I have worked out that is because I have been distributing the app via DropBox with out zipping it.
Try putting the app in a zip file before uploading to DropBox. Instruct the users to download the zip file, unzip it and install the app.
My guess is that DropBox is stuffing up some of the files in the app package.