PopupControl called by other controls

When I select other control buttons in my form the popup I'm using (which works just fine with it's intended controls) pops up under a javascript 'message box'...  Code below and any help is apreciated.

CODE

<!-- -----------------Memo Field Controls ------------------ -->
<td align="center" valign="middle">
   <asp:Button ID="MemoBtn" runat="server" 
               Text="MEMO" 
               Width="80px" 
               BackColor="AntiqueWhite" 
               ForeColor="DarkBlue" 
               ToolTip="Select to enter Memo-Field data. . ." />
</td>
<asp:Panel ID="MemoPopup" runat="server" 
           Height="80px" Width="400px"> 
   <asp:UpdatePanel ID="UpdatePanel1" runat="server"> 
   <ContentTemplate>                                                                       
   <asp:TextBox ID="MemoText" runat="server" 
                Width="400px" textmode="MultiLine" height="80px" Wrap="true">              
   </asp:TextBox>   
   &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
   <asp:Button ID="Memoclear" runat="server" 
               OnClick="Clearmemo" Text="Clear" />
   <asp:Button ID="Memodone" 
               runat="server"  Text="Done" 
               OnClick="EvalMemo"/>
   </ContentTemplate> 
   </asp:UpdatePanel> 
   </asp:Panel>
   <asp:PopupControlExtender ID="PopupControlExtender1" runat="server" 
                             TargetControlID="MemoBtn" 
                             PopupControlID="Memopopup" 
                             Position="Left" 
                             CommitProperty="value" 
                             OffsetX="23" > 
   </asp:PopupControlExtender>
   <!-- -----------------Memo Field Controls ------------------ -->   

MESSAGEBOX Function

    Public Shared Sub Client_Alert(ByVal sMessage As String, Optional ByVal sURL As String = "")
        On Error Resume Next
        Dim str As String, sb As New StringBuilder(Len(sMessage) * 5)
        Dim P As System.Web.UI.Page = CType(System.Web.HttpContext.Current.Handler, System.Web.UI.Page)
        sMessage = sMessage.Replace(Chr(0), "")
        For Each c As String In sMessage : sb.Append("\x" & Right("0" & Hex(Asc(c)), 2)) : Next
        str = vbCrLf & "<script language=javascript>" & vbCrLf
        str = str & "    alert('" & sb.ToString & "');" & vbCrLf
        If Len(sURL) > 0 Then str = str & "    window.location='" & sURL & "';" & vbCrLf
        str = str & "</script>" & vbCrLf
        P.ClientScript.RegisterStartupScript(P.GetType, "", str)
    End Sub