multithreading - InvalidCastException when using webbrowser and threads in c# -

when trying use webbrowser component inside backgroundworker.dowork function , got exception :

system.invalidcastexception unhandled user code

http://i.stack.imgur.com/ejft3.jpg

here's code :

void m_oworker_dowork(object sender, doworkeventargs e)     {         //note : never play ui thread here...         string line;          //time consuming operation         while ((line=sr.readline()) != null ){              int index = line.indexof(":");             htmldocument doc = web.document;             thread.sleep(1000);             m_oworker.reportprogress(cnt);              //if cancel button pressed while execution in progress             //change state cancellation ---> cancel'ed             if (m_oworker.cancellationpending)             {                 e.cancel = true;                 m_oworker.reportprogress(0);                 return;             }              cnt++;         }          //report 100% completion on operation completed         m_oworker.reportprogress(100);     } 

or way use thread in c# ?

cause when use thread.sleep method in main gui freezes !!

the webbrowser doesn't being accessed other threads. try passing in runworkerasync() this:

    private void button1_click(object sender, eventargs e)     {         htmldocument doc = web.document;         m_oworker.runworkerasync(doc);     }      void m_oworker_dowork(object sender, doworkeventargs e)     {         htmldocument doc = (htmldocument)e.argument;          //note : never play ui thread here...         string line;          //time consuming operation         while ((line = sr.readline()) != null)         {             int index = line.indexof(":");              thread.sleep(1000);             m_oworker.reportprogress(cnt);              //if cancel button pressed while execution in progress             //change state cancellation ---> cancel'ed             if (m_oworker.cancellationpending)             {                 e.cancel = true;                 m_oworker.reportprogress(0);                 return;             }              cnt++;         }          //report 100% completion on operation completed         m_oworker.reportprogress(100);     }