Could not open an app in mendix modeler

I have created a mobile app in web, but I was not able to open it in mendix modeler. Its throwing following error. And i am not getting an option to select local folder while opening the app. Can anyone help me on this?  
1 answers

Please search the forum for the follwoing term:

"Object reference not set to an instance of an object"

THere are quite a number of questions on this subject with some answers that might be helpfull in your case.