You are comparing strings with greater than and less than logic when you need to use numeric types to do this comparison, like this:
Dim number As Single
If Single.TryParse(lbscore.Text, number) Then
' Do comparison logic
If number < 75 Then
Message.Text = "Your score does not meet minimum requirement"
ElseIf number >= 75 Then
Message.Text = "Congratulations; you have passed the test"
End If
Else
' Could not convert text from lbscore to a Single
Message.Text = "Error trying to determine your score!"
End If