I had reports and crash dumps from users who were crashing directly on login.
The position of the crash is llnotify.ccp inside
void LLNotifyBox::moveToBack()
at
front->mNextBtn->setFocus(TRUE);
Looking at the dump showed that the returned "front" wasn't a LLNotifyBox but a LLGroupNotifyBox.
The error goes down to a bad assumption inside LLNotifyBox * LLNotifyBoxView::getFirstNontipBox() const where the function expects all childs to be of type LLNotifyBox which is obviously not true because group notifications are also added to gNotifyBoxView (see llgroupnotify.cpp);
The attached patch is more like a band aid or a sample to highlight the problem, someone who knows what he's doing will probably come up with a better method.
As a side note, there's also an assumption in moveToBack which is not true
// assuming that moveToBack is only called by clicking the next button,
// we give focus to the next next button
as the function is now called when a new box opens (and in those cases on login without any user interaction).
This is a dry patch at the moment (not tested or verified).