VBA: Using Symbols

I have a problem, when I have if-else statements that specifies the value of my combo-box, I encountered error on symbols (greek letter raw to be specific)
It only displyed ? as seen in the incomplete program. Any help would be appreciated.

Private Sub ComboBox1_Change()

If ComboBox1.Value = "Pa" Then



ElseIf ComboBox1.Value = "Pb" Then



ElseIf ComboBox1.Value = "G" Then



ElseIf ComboBox1.Value = "R" Then



ElseIf ComboBox1.Value = "T" Then



ElseIf ComboBox1.Value = "M" Then



ElseIf ComboBox1.Value = "a" Then



ElseIf ComboBox1.Value = "Pb" Then



ElseIf ComboBox1.Value = "?a" Then







End Sub