In PowerShell, this method returns a SearchResult object if only one object is found, instead of a SearchResultCollection. If you want to check the number of returned objects via the Count property of SearchResultCollection, you need to code around this if the search might return only one object.

this will only return the first 1000 items unless you set the pagesize.

            // Connect to LDAP

            AuthenticationTypes authTypes; // Authentication flags.
            authTypes = AuthenticationTypes.Signing | AuthenticationTypes.Sealing | AuthenticationTypes.Secure;

            string domainAndUsername = domain + @"\" + user;

            DirectoryEntry oAuthedEntry = new DirectoryEntry(ldapConnectionString, domainAndUsername, pwd, authTypes);

            // Create new DirectorySearcher instance
            DirectorySearcher search = new DirectorySearcher(oAuthedEntry);

           // Set search criteria

            search.Filter = "(objectCategory=user)";

            search.PropertiesToLoad.Add("displayName");                             // name
            search.PropertiesToLoad.Add("physicalDeliveryOfficeName");      // location
            search.PropertiesToLoad.Add("telephoneNumber");                    // phone number
            search.PropertiesToLoad.Add("mobile");                                     // mobile            
            search.PropertiesToLoad.Add("mail");                                        // email address
            search.PropertiesToLoad.Add("msDS-UserAccountDisabled");   // account status  
            search.PropertiesToLoad.Add("title");                                        // title
            search.PropertiesToLoad.Add("ms-DS-UserAccountAutoLocked");     // locked

            // Perform the search
            SearchResultCollection results = null;
            try
            {
                results = search.FindAll();
            }
            catch (Exception searchEx)
            {
                throw new Exception("Error obtaining users results. ", searchEx);
            }