Upload a file using C# as a Server method

I will be using a server C# method upload files for migration from a legacy PLM system.

C# method, in lieu of Batch Loader, is to used to allow more logic to be applied to the file uploading. Based on https://community.aras.com/f/development/3741/ I have simplified the code to

Innovator inn = this.getInnovator();

Item fileUpload = inn.newItem("tmp");
// File 1
Item file1 = inn.newItem("File", "add");
file1.setProperty("filename", "Comments Against V1.0.xls");
file1.setProperty("actual_filename", @"C:\Program Files (x86)\Aras\Innovator\Innovator\Server\temp\0000000000eb34");
file1.setProperty("checkedout_path", @"C:\Aras");
Item located = file1.createRelationship("Located", "add");
located.setProperty("related_id", "67BBB9204FE84A8981ED8313049BA06C"); // default vault
fileUpload.appendItem(file1);

//fileUpload.removeItem(fileUpload.getItemByIndex(0));
IomFactory factory = new IomFactory();
Aras.IOME.CheckinManager cm = factory.CreateCheckinManager(fileUpload);
return cm.Checkin(1);

Which returns an error, typically 

SOAP-ENV:ServerFile with id 8F904AA99D69489BAE6F948D6A679767 cannot be found in any of its containers.File with id 8F904AA99D69489BAE6F948D6A679767 cannot be found in any of its containers.

Any suggestions?