Try it like this:
Dim tempCheck as string = "1st BARITONE"
Dim GoodOne as Boolean = False
Select Case True
Case tempCheck.Contains("CORN")
GoodOne = True
Case tempCheck.Contains("HORN")
GoodOne = True
Case tempCheck.Contains("BAR")
GoodOne = True
Case tempCheck.Contains("TROM")
GoodOne = True
Case tempCheck.Contains("EUP")
GoodOne = True
Case Else
GoodOne = False
End Select
SELECT CASE doesn't work on strings like this (you have to compare string to a string, in this case you compare to a boolean). It does work on Booleans compared to booleans