App Inventor has a 5MB limit on how big your AIA file can be
(http://twodogapps.com/?page_id=686#MakingAIA Click here). This has to do with how the build server handles projects,
and while you may be able to get by with a file that’s bigger, the likelihood is that your project won’t compile every time. Reducing the size of an AIA file really isn’t that difficult. Of course, the answer to the main question here is that you have to reduce the size of that AIA… But how?
First, what are assets? They’re pictures, sounds, videos, graphics etc. that you’ve added to your project.
Too Voluminous – If you have uploaded many, many assets to your project, you’ll have to remove some of them, or use the other techniques mentioned below. Do you really need all of those assets? Try to reuse items if you can.
Too Big – This is a pretty simple item… you have a 5MB limit, and App Inventor takes at least 1.5 of those megabytes just to work. If you add a 7MB video, your project will fail. But, you say, “I need that video!” The best way to handle this is to load the video from the web the first time the app runs. Taifun and Hossein have solutions on the App Inventor forum on how to do this. Rather than include the video with the APK, download it when the app first runs.
For More Info Check this
http://twodogapps.com/?page_id=686#ShrinkingAIA
solved Maximum size limit restriction of MIT App Inventor project