Qwt Legend Parent

[BlackFoXX]

Hi,
I have some trouble with my QwtLegend. Every time I try to add a new QwtPlotCurve the program terminates with the folling error:

QObject::setParent: Cannot set parent, new parent is in a different thread
monitor: ../../src/xcb_lock.c:77: _XGetXCBBuffer: Assertion `((int) ((xcb_req) - (dpy->request)) >= 0)' failed.
Aborted

Posting Code is not that simple, because it's a quite big project. In general I created a subclass of QwtPlot and in this class i call

addCurve( Object* o) {
o->getCurve()->attach(this);
}

addCurve( Object* o) {
o->getCurve()->attach(this);
}

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where "Object" is a custom object.

I hope someone can help me.
Thanks in advance.

Jones