You can not export the file; that means you cannot create an aia file. That is a problem. To migrate the Project to the code.appinventor.... server, you need to create an aia and load that aia to the code.appinvventor...server. You cannot migrate unless you have an aia. Otherwise you have to re-code everything.
Do you have an old Project aia? Migrate that.
Hello,
I have the same problem: I can't load the project because probably it is too big. Server returns me the error: "Server error: could not load file. Please try again later!".
I tried more times, but I had the same error.
How can I access the project for modifying and simplifying it?
Thanks in advance
Load your latest .aia export into the code.appinventor.mit.edu server,
and trim the fat from your Media folder.
i have the same problem,something went wrong.have a simple project just for test and a get the message
" Server error : could not load the file. Please try again". I try a new project,restrat pc ,mit, but nothing.I think is something with my account.Please can you check.I also have a bug report message in the first time the problem appears.
Please can you check my account something is stop woriking.I cannot save ,modify any of my project!
Thankfully the problem was slow network speed!..The only think is that the aia file was have issues..and report bug message apears evrytime i import the file..Fortunately i have i backup some steps behind but it's not a problem 
How many MB is the .aia export file?
The aia is 10,46Mb until now..
That's too big for the ai2.appinventor.mit.edu server.
If you can't put it on a diet (shrink Media files, reduce redundant Screens and blocks), try the more expensive code.appinventor.mit.edu server.
Take frequent backups of .aia exports, just in case you hit another wall.
Is it ? ai2 server can handle up to 30mb apk
30mb .apk might work if you can get the project into the server across the network.
A bigger upload from an .aia file is potentially at more risk from an upload time out, right?
The ai2 server has an attention span of what, a minute?
P.S. One of the benefits of being a pessimist, is that you're rarely disappointed.
What is the difference between ai2.appinventor.mit.edu and code.appinventor.mit.edu ?
code.appinventor can process Projects of aia < 50 MB . It is run on the Amazon server. Allows a longer time out.
ai2.appinventor can process Projects of aia < 30 MB. It is usually run on MIT server. Times out after a minute.
When either server is busy, sometimes the Server error. Usually try again later will allow compiling when the server balancers kick in and provide more capacity.
Correction: The server runs in Google App Engine, which is responsible for the hard one minute timeout.