Multi-threaded application using IQueryService

Hello,

I have a very basic multi-threaded application written in C# that uses the DFS IQueryService to perform a very simple DQL query. From time to time, we'll get "Authorization Failed" errors and we cannot find out what is causing the problem. I'm looking for a good place to start to track down the problem, i.e. log files, setting log levels, etc.. I can certainly post the code I'm using.