Lio,
there are potentially 2 problems here:
- the request thread is using too much memory/has a memory lead
- the size of the file is too large.
i know you are having the second problem, not sure about the first. it's possible that the second problem is being reported to you with a mis-leading message.
as for the file size, i am assuming that you are trying to store the file directly on a row in the table. Remember that on GAE, when using the datastore, each row is limited to 1MB total, and any given field is limited to 1MB (which you can only achieve if the row contains 1 field).
To grow past this limitation, look into the GAE blobstore for storing large files. you also can write tools that upload the file to some other location (google cloud storage, amazon S3) and store the link to the file in your table.
hope that helps!
cfh