Button not initialized, almost solved.
Thank you Klaus and Theera for your replies.
Learning to create buttons in code, not the designer, is a little in the future for me yet. As for Button not initialized, the error only appears when Stepping (F8).
I tried placing a break point in btnEvent_Click at "If lblResult.Text.Length > 0 Then". Press F5, run the program on the smart phone, make a mistake, press the "BS" key, the debugger stops at the break point, press F8 to step, all OK, press F5 to run, again all OK.
The problem of the colour change, yes, the test string in the source code is "O K" (Capital O, space, Capital K). The program was only looking for what it was told to look for. My mistake!