unity project freezes on one machine but not another

I have two machines one opens my unity project fine, the other crashes with null exception when I press play. It works fine on the other machine. The file is on dropbox so it’s the same file. What would cause this. Do I have to reinstall the entire 1 GB Unity or is there some way to reset the preferences.

Are you using meta files? I find if I use the default cache files vs. meta I can get problems in Dropbox. If you’re not already using meta files I’d recommend switching over first, then deleting both Library and Temp folders and anything in the root of the project. This is basically stripping down the game to it’s essentials. Then give it a try. If it still doesn’t work then my next step would be to re-install.