>>>Your app. needs to be able to find this DLL. I usually add the DLL to the project (not as a reference, just to the project) then select it and set "Copy to Output Directory" to "Copy always".
>>
>>Do you know how should I figure out the problems? I've been debugging the test. When I come up to the Invoke1 line I saw a call to Request.Dispose method (request is a separate class that implements IDisposable interface) and then the test ended. So, I assume that this call somehow interrupted the whole thing.
>
>If Request.Dispose() fired unexpectedly then it's a sure sign that your code threw an uncaught exception - which was probably the failure to load the DLL.
>You should add your own try/catch block.

Here is my current code:

  internal String RestoreData(String columnValue, String convertCode)
        {   
            String result = "";
            String invoke = "gethash".MakeTag("func") + (convertCode + this.nClientNumber.ToString() + "SELECT version FROM metadata").MakeTag("data");
            String translate = "";
            try
            {
                translate = Invoke1(invoke);
                if (translate.Left(4) == "OK :")
                {
                    invoke = "decryptdata".MakeTag("func") + columnValue.MakeTag("data") + translate.Substring(4).MakeTag("key");
                    result = Invoke1(invoke);
                }
            }
            catch
            {
                Logging.Log(1, "Using ww_local.dll generated an exception...");
            }
            return result;
        }

As you see, I have try/catch here. But it's getting by-passed and I see a call of Dispose method of the Request class.