ironPython - python socket file transfer, typeError

I'm trying to send a binary file from a client that runs on ironPython 2.7.4 to a server that runs on cpython 2.7.6 on a linuxbox. I followed this example, however when the server starts writing the file (first call to f.write), I get an Error:

TypeError: must be string or buffer, not int

Here the I think relevant pieces of the code.

server:

def recvall(self, count):

    msgparts = []
    while count > 0:
        newbuf = self.conn.recv(count)
        if not newbuf: return None
        msgparts.append(newbuf)
        count -= len(newbuf)

        #print "%i bytes left" % count

    return "".join(msgparts)

#receive file, write out
f = open(fname, 'wb') 
chunk = self.recvall(1024)
while (chunk):
    f.write(1024) #<-- error happens here.
    chunk = self.recvall(1024)

    f.close()

client:

f = open(fname, 'rb') 
chunk = f.read(1024)
while (chunk):
    self.conn.send(chunk)
    chunk = f.read(1024)

f.close()

conn is the socket connection - this works, I can transfer pickled dicts successfully.

Any hints?

thanks and regards, Dominic