Most instances of Developers getting that error response is due to issues with the Project's images (usually large images) that the app cannot handle. A rule is, make your images 'right sized.' Do not rely on the ability of the compiler to 'make images fit' ... that uses lots of processing power and can cause your app to fail.
Here are some resources to help you learn to use the AI2 tools. A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook http://www.appinventor.org/book2 ... the links are at the bottom of the Web page. The book 'teaches' users how to program with AI2 blocks.
Store this in a text file, then return it with a file component. Or just store it as an image, most likely this will take up less space than a base64 text of the image.
Very Important question, please help us - did you put that file in your Project Media or did it just appear all by itself. We have another AI User with a similar issue.
Sorry to bother you again, MIT is trying to get to bottom of this issue and would appreciate more info:
Your OS and OS version
Your Browser and Browser Version
... trying to see if there is a common denominator amongst those affected.