I've been getting the following error message recently when uploading a file using the REST API:
Microsoft.SharePoint.Client.InvalidClientQueryException - The request message is too big. The server does not allow messages larger than 262144000 bytes.
I've been using this method to upload files both small and large to SharePoint for a while now and never come across this error before. I've been looking at some articles and it appears this message could appear when uploading a file using CSOM. In this case I am not, I do you use csom to add permissions and perform some other small updates.
This is the code used for the REST call: http://sharepointfieldnotes.blogspot.co.uk/2014/07/uploading-large-documents-into.html (Uploading Large Documents With REST)