I have encountered an error that I don't quite understand. I am setting up a website for some friends of mine and I'm trying to setup an admin page that will allow future users to be assigned permissions after the site is deployed. I hit a few errors during the creation that had to do with my general lack of coding skills, but the error I'm getting now I don't think I caused. Here is the error that I'm getting:

Server Error in '/NstazMainSite/Nstaz' Application.

---

Conversion failed when converting from a character string to uniqueidentifier.

Line 16: 
Line 17:         Mycon.Open()
Line 18:         Mycmd.ExecuteNonQuery()
Line 19:         Mycon.Close()
Line 20: 

[SqlException (0x80131904): Conversion failed when converting from a character string to uniqueidentifier.]
   System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) +404
   System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning() +412
   System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) +1363
   System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async) +2840828
   System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) +504
   System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +327
   Admin_UserSettings.btnAssign_Click(Object sender, EventArgs e) in C:\inetpub\NSTaZ\NstazMainSite\Nstaz\Admin\UserSettings.aspx.vb:18
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +154
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3691

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1

Here is the .aspx and .aspx.vb that generated this error:

<%@ Page Title="User Config Settings" Language="VB" MasterPageFile="~/Site.Master" AutoEventWireup="false" CodeFile="UserSettings.aspx.vb" Inherits="Admin_UserSettings" %>


<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" Runat="Server">


<p class = "clearRead">


This Page will contain an API connection to allow the changing of user groups and permissions.<br />
May take a bit as this is new to me.


    </p>
     <br />






    <asp:Label ID="lblUsers" runat="server" Text="Users: "></asp:Label>
    <asp:DropDownList ID="ddlUser" runat="server" DataSourceID="appUsersDS"
        DataTextField="UserName" DataValueField="UserId">
    </asp:DropDownList>


     <br />


    <asp:Label ID="lblRoles" runat="server" Text="Role to assgin: "></asp:Label>
    <asp:DropDownList ID="ddlRole" runat="server" DataSourceID="appRolesDS"
        DataTextField="RoleName" DataValueField="RoleId">
    </asp:DropDownList>


     <br />


    <asp:Button ID="btnAssign" runat="server" Text="Assign Role" />








    <asp:SqlDataSource ID="appUsersDS" runat="server"
        ConnectionString="<%$ ConnectionStrings:ApplicationServices %>"
        SelectCommand="SELECT [UserName], [UserId] FROM [vw_aspnet_Users]"></asp:SqlDataSource>


    <asp:SqlDataSource ID="appRolesDS" runat="server"
        ConnectionString="<%$ ConnectionStrings:ApplicationServices %>"
        SelectCommand="SELECT [RoleName], [RoleId] FROM [vw_aspnet_Roles]"></asp:SqlDataSource>
    

<asp:SqlDataSource ID="appUsersRolesDS" runat="server"
        ConnectionString="Server=VHS03.Jonny11b.com; Database=nstaz_AppData; User ID=*******;Password=*******;"
        SelectCommand="SELECT [UserId], [RoleId] FROM [vw_aspnet_UsersInRoles]"
        UpdateCommand ="UPDATE aspnet_UsersInRoles SET RoleId = @NewRole WHERE (UserId = '@sUser')"
        InsertCommand="INSERT INTO aspnet_UsersInRoles(UserId, RoleId) VALUES ('@sUser', '@NewRole')">
    <InsertParameters>
        <asp:Parameter Name="sUser" />
        <asp:Parameter Name="NewRole" />
    </InsertParameters>
    <UpdateParameters>
        <asp:Parameter Name="NewRole" />
        <asp:Parameter Name="User" />
    </UpdateParameters>
    </asp:SqlDataSource>




</asp:Content>

Partial Class Admin_UserSettings
    Inherits System.Web.UI.Page

    Protected Sub btnAssign_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAssign.Click


        Dim Mycon As Data.SqlClient.SqlConnection
        Dim Mycmd As Data.SqlClient.SqlCommand
        Dim NewRole As String = ddlRole.SelectedValue
        Dim sUser As String = ddlUser.SelectedValue

        Mycon = New Data.SqlClient.SqlConnection("Server=VHS03.Jonny11b.com; Database=nstaz_AppData; User ID=*******;Password=*******;")
        Mycmd = New Data.SqlClient.SqlCommand(appUsersRolesDS.InsertCommand, Mycon)

        Mycon.Open()
        Mycmd.ExecuteNonQuery()
        Mycon.Close()

    End Sub

End Class