Error while creating Embedded Canvas

Hi ROOTers,

I am building a standalone Qt application and I'm trying to implement an embedded canvas as an Online Display in a tab of a QTabWidget. I inserted a QWidget in the tab and got it's id with:

Int_t wid = gVirtualX->AddWindow((ULong_t) ui->displayWidget->winId(), 1050,650);

And I'm creating a TCanvas using:

TCanvas *c1 = new TCanvas("Display", 1050,650, wid);

I have also included in my main the lines TApplication *gMyRootApp = new TApplication("My ROOT Application", &argc, argv);
gMyRootApp->SetReturnFromRun(true);

according to this how to:
http://root.cern.ch/drupal/content/how-embed-tcanvas-external-applications

However I seem to get an error
Error in <RootX11ErrorHandler>: BadWindow (invalid Window parameter)

I thought it was the QWidget, so I created a main window to embed the canvas. When I did this the code compiled, but on execution no canvas appeared and each time I exit the application I get a segfault.

Any ideas on how to proceed?

Thanks in advance,
Nikos

-- 
Nikos Karastathis
PH-UAT - CERN
40-2-D19
+41 22 76 71162