Cannot Get A SearchResponse Sometimes

Question

I am using the System.DirectoryServices.Protocols library to connect to an LDAP source. I have not had any issues with eDirectory, but I am having some trouble with Active Directory.

The Active Directory server is running on a Windows 2003 machine.

Here's a summary of the code I've been using (try catches were removed):
LdapConnection con = new LdapConnection(new LdapDirectoryIdentifier(Server, Port));
con.SessionOptions.SecureSocketLayer = false;
con.Credential = new NetworkCredential(Username, Password);
con.AuthType = AuthType.Basic;
con.Bind();
SearchRequest request = new SearchRequest(DN,FILTER,System.DirectoryServices.Protocols.SearchScope.Subtree);
SearchResponse response = (SearchResponse)con.SendRequest(request); //this is the line that throws a DirectoryOperationException

Here's the stack trace from the exception:
System.DirectoryServices.Protocols.DirectoryOperationException was caught
  Message="An operation error occurred."
  Source="System.DirectoryServices.Protocols"
  StackTrace:
       at System.DirectoryServices.Protocols.LdapConnection.ConstructResponse(Int32 messageId, LdapOperation operation, ResultAll resultType, TimeSpan requestTimeOut, Boolean exceptionOnTimeOut)
       at System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryRequest request, TimeSpan requestTimeout)
       at System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryRequest request)
       at <the line that I call from>

Here's the message that was stored in the response of the DirectoryOperationException:
"00000000: LdapErr: DSID-0C090627, comment: In order to perform this operation a successful bind must be completed on the connection., data 0, vece"
I think this error message is a little fishy because when I debug line by line, it successfully passes the con.Bind() line.

Now it continues like this for an hour or so. Afterwards, I am able to authenticate succesfully every time. In summary, it works sometimes. I thought the server might have gone down. However, I can login and browse succesfully using a third party LDAP client. This gives me strong reason to believe that it's not the servers issue, but an issue with my code.

If I am missing any information I will try my best to get it for you as quickly as possible. Thank you in advanced for your help!