I am succesfully connecting to an external SFTP site, and pulling some files into Netsuite using the "Connection.download" API. However, now I am trying to upload some files from the file cabinet using "Connection.upload", and the connection goes thru, but the file is not uploaded due to this error:

{"type":"error.SuiteScriptError","name":"UNEXPECTED_ERROR","message":null,"id":"99fb0517-6f26-417c-aa90-94d056008d24-2d323032332e31302e3130","stack":["anonymous(N/file)","execute(/SuiteScripts/TSM Scripts/TSM - Export Inventory Stock File.js:25)"],"cause":{"type":"internal error","code":"UNEXPECTED_ERROR","details":null,"userEvent":null,"stackTrace":["anonymous(N/file)","execute(/SuiteScripts/TSM Scripts/TSM - Export Inventory Stock File.js:25)"],"notifyOff":false},"notifyOff":false,"userFacing":false}