exception Erro: the underlying provider failed on open

[mauricio_12_85]

exception Erro: the underlying provider failed on open on code

private void button1_Click(object sender, EventArgs e)
{
try
{

TESTEEntities obj = new TESTEEntities();

user objuser = new user();

objuser.nome = textBox1.Text;

obj.AddTouser(objuser);
obj.SaveChanges();
}
catch ( Exception ex)
{
MessageBox.Show(ex.Message);
}

[Shalex]

"Underlying provider failed on open" is a general high-level exception which doesn't tell us about the actual problem. Could you please run your application in the debug mode and post here the exact text of the inner exception with its call stack?