WINCE print to Zebra QL220 works exactly once - printing

Question

I use the code below to print to a Bluetooth Zebra QL220 Plus printer from a test form. (The test project was set up as I was experiencing this problem in the main project).
The first time I ran this program it printed correctly.
Running the exact (unchanged) code again does absolutely nothing.
No matter what I do:
Pull the battery from the Printer
Hard reboot the WT41N0 device
Reconnect the Printer using BTExplorer
Restart the program.
The following code steps thru in the debugger, but does absolutely nothing.
Dim wSerialPort As SerialPort = New SerialPort()
wSerialPort.BaudRate = 19200
wSerialPort.Handshake = Handshake.XOnXOff
wSerialPort.DataBits = 8
wSerialPort.Parity = Parity.None
wSerialPort.StopBits = StopBits.One
wSerialPort.PortName = "COM9:"
wSerialPort.ReadTimeout = 500
wSerialPort.WriteTimeout = 500
wSerialPort.Open()
wSerialPort.Write("! 0 200 200 600 1" & vbCrLf)
wSerialPort.Write("LABEL" & vbCrLf)
wSerialPort.Write("CONTRAST 0" & vbCrLf)
wSerialPort.Write("TONE 0" & vbCrLf)
wSerialPort.Write("SPEED 5" & vbCrLf)
wSerialPort.Write("PAGE-WIDTH 419" & vbCrLf)
wSerialPort.Write("T 7 1 40 141 Hello" & vbCrLf)
wSerialPort.Write("FORM" & vbCrLf)
wSerialPort.Write("PRINT" & vbCrLf)
wSerialPort.Close()
I had one idea that I might have the page size wrong and that the printer was stopped over the gap between labels, but reloading the label roll had no effect.
Any ideas?
Hardware:
Printer QL220 Plus
Device WTN41N0
VS2008 using .Net 3.5
Dev OS Windows 8.1

Answer 1

Since it seems that the printer uses the RFCOMM protocol, emulating a serial port you may try to replace the printer with a bluetooth-enabled PC and use a terminal app to see what is received the first time and then the following ones, to understand if your device is sending data the second time it prints and if there is something different compared to the first send.