Customer MembershipProvider

   I've implemented a simple MembershipProvider and I'm only implementing the ValidateUser method.  When the method is called I get the following error:

An EntityManager can only execute on a single thread. This EntityManager is authorized to execute on the thread with id=’12’; the requested operation came from the thread with Id=‘10’.
Consider calling the EntityManager’s asynchronous methods; they work safely on background threads managed by DevForce. 
You may have to disable this cross-thread checking for specific reasons such as automated testing. Please review our documentation on multi-threading issues and the EntityManager.AuthorizedThreadId property.

Here is the Method:　

public override bool ValidateUser(string username, string password){
ACTContext _dc = new ACTContext();
var query = _dc.actMembers.Where(m => m.UserName == username && m.Password == password);
bool flag = false;
_dc.ExecuteQueryAsync(query, (s) => {s.Completed += (o, args) => {
  if (args.HasError)args.MarkErrorAsHandled();
  if (args.Results != null)
  flag = true;
};
});
return flag;}

What am I missing?

RL