C# - Insert GUID Into SQL Table?

I'm using ASP.Net/C# and I have a form that allows people to add information into a table and along with it I want to collect the Current Users GUID and insert it.

I have a field setup (UserID) as a unique identifier and I have the following code:

protected void Page_Load(object sender, EventArgs e)
{
MembershipUser currentUser = Membership.GetUser();
Guid temp = (Guid)(Membership.GetUser(User.Identity.Name).ProviderUserKey);
Guid @currentUserID = temp;
}
SqlConnection con = new SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\ASPNETDB.MDF;Integrated Security=True;User Instance=True");
SqlCommand cmd;
protected void Button1_Click(object sender, EventArgs e)
{
con.Open();
cmd = new SqlCommand("insert into Accom (UserID) values('" + @currentUserID + "')", con);
cmd.ExecuteNonQuery();
}

I basically want to link the variable to the Database how as the above gives errors.