Permission Denied on Key Preview

Env -- VB6/ win7

Sir,

I have designed a VB6 form on with I have made the key preview on. I want my users to change the focus on next control and select the whole text on that control on press of ENTER . For this I have written this

Private Sub Form_KeyUp(KeyCode As Integer, Shift As Integer)
If KeyCode = vbKeyReturn Then
KeyCode = 0
SendKeys "{TAB}"
sendKeys "+{END}"
End If
End Sub


This code was working find few days before but suddenly it stopped working and giving error as "PERMISSION DENIED"
Pl. help or if u have any other way get the work done pl. give the code.
Thanks