The content range header should be in the following format:
Content-Disposition: form-data; name="fileContent"; filename="myfile.dat"\r\n
Content-Type: binary/octet-stream\r\n
Content-Range: 0-4/5\r\n
\r\n
Let me know if that helps, there are full samples in the appendix of the documentation with difference scenerios.
Regards,
Barry R.