[agraham]

It works fine for me if you move the button enabling/disabling code after the radio button setting but I'm not sure why.

Sub ShowData
    Label1.Text="Q"&(AnsRec+1)&". "
    If Answer(AnsRec)=0 Then
        For i=1 To 5
            Control("RadioBtn"&i).Checked=False
        Next
    Else
        Control("RadioBtn"&Answer(AnsRec)).Checked=True
    End If
    If AnsRec=0 Then
        PrevBtn.Enabled=False
        NextBtn.Enabled=True
    Else If AnsRec=5 Then
        PrevBtn.Enabled=True
        NextBtn.Enabled=False
    Else
        PrevBtn.Enabled=True
        NextBtn.Enabled=True
    End If    
End Sub

EDIT : Got it! I didn't originally get the full import of Erel's explanation. Disabling the Prev button causes the focus to move from the Prev button back to the Radio Button. However AnsRec has already been decremented so Radio_Click thinks this extra click it is a new value for Q1 and stores what was the value for Q2 as Q1's value overwriting the previous value. Putting the disabling later ensures that the correct Radio Button for Q1 has already been selected so that it still overwrites the answer, but with the correct one this time!