Cannot access a closed file exception? [Using binary Reader]

Any Idea,
I get an error randomly when I try to ReadBytes using Binary Reader. See below code

Exception: Cannot access a closed file.
try {
                if (inputStream == null) return;
                using (BinaryReader br = new BinaryReader(inputStream)) {
                    int buffSize = 1048576;
                    byte[] buf = null;
                    using (BinaryWriter binaryWriter = new BinaryWriter(File.Open(strFileName, FileMode.Create))) {
       &nbs ...