Thanks for all the help guys - seriously appreciated! I found the error and yes indeed it wasn't with the select case at all. The cause: I was receiving a DTMF tone through a dedicated DTMF receiver IC which required a polling of a status pin which would trigger my code to shift out the tone value from the receiver IC in 4 bit format. Problem for me was that initially that value would be correct (as my debugging highlighted) and the select case was receiving this expected value (which my testing highlighted), but because there was no pause in the code anywhere for many tones, the code would go straight back to polling and receiving right after the select case execution which turned out to be too fast and the "tone value" register in the receiver IC must default to 15 after being read. Because the status pin still flagged a valid tone receive, my code would read this value (15) and act on it with the "select case" code in question and my output (a light globe for testing purposes) would only visibly display the result of the "15" value every time thereby leading me to erroneously assume the select case was causing the issue. Duh - apologies for any time wasted.

Thanks again,

Troy