active directory problem

[Tunga Torgal]

I have the following c# code to find an employee's copmany wide ID from its
given username... It is being used from an ASP.NET page...

Code works fine in much of the situations.. But sometimes it gives "an
operation error occured.." error..
What is the reason of it? Is there anyone having an idea???

Here is the code:

DirectoryEntry dfDNC = new DirectoryEntry(path_string);
DirectorySearcher oDS = new DirectorySearcher(dfDNC);
oDS.PageSize = 10;
oDS.SearchScope = System.DirectoryServices.SearchScope.Subtree;
oDS.Filter = "(&(objectclass=user)(objectcategory=person)(name= " + UserName
+ "))";
oDS.PropertiesToLoad.Add("employeeID");
SearchResult oRes = oDS.FindOne();
return oRes.Properties["employeeID"][0].ToString();