Qt assignment segfault

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1224452432 (LWP 16227)]
0xb789271d in ?? () from /usr/lib/qt4/libQtGui.so.4
(gdb) bt full
#0  0xb789271d in ?? () from /usr/lib/qt4/libQtGui.so.4
No symbol table info available.
#1  0xb78c6f3c in QWidget::insertAction () from /usr/lib/qt4/libQtGui.so.4
No symbol table info available.
#2  0xb78c710a in QWidget::addAction () from /usr/lib/qt4/libQtGui.so.4
No symbol table info available.
#3  0x08054604 in MainWindow::createContextMenu (this=0xbf91f5c0)
    at mainwindow.cpp:216
No locals.
#4  0x08055a6b in MainWindow (this=0xbf91f5c0) at mainwindow.cpp:15
No locals.
#5  0x080536a1 in main (argc=Cannot access memory at address 0x0
) at main.cpp:8
        app = <incomplete type>
        mainWin = {<> = {<No data fields>}, <Ui::MainWindow> = {<Ui_MainWindow> = {
      newAction = 0x804d7d5, openAction = 0xb71942d5, saveAction = 0x8066318, 
      saveAsAction = 0xb71712f4, exitAction = 0x8066004, cutAction = 0xb7f88ca0, 
      copyAction = 0xb728cff4, pasteAction = 0x804fda0, deleteAction = 0x805db00, 
      findAction = 0xbf91f608, goToCellAction = 0xb7194440, 
      selectRowAction = 0x8066000, selectColumnAction = 0xb7f88ca0, 
      selectAllAction = 0xbf91f628, recalculateAction = 0x804fdf7, 
      sortAction = 0x804fda0, showGridAction = 0x0, autoRecalcAction = 0x806670c, 
      aboutAction = 0x7c838c, aboutQtAction = 0xffff, separatorAction = 0x1, 
      centralwidget = 0xbf91f638, hboxLayout = 0x804fe0f, spreadsheet = 0x8089938, 
      menubar = 0xb7f896c8, fileMenu = 0xbf91f648, editMenu = 0x805db95, 
      selectSubMenu = 0xf63d4e2e, toolsMenu = 0x8066190, optionsMenu = 0xbf91f658, 
      helpMenu = 0x804e729, fileToolBar = 0xb788eb80, 
      editToolBar = 0x0}, <No data fields>}, static staticMetaObject = {d = {
      superdata = 0x8066780, stringdata = 0x805ea20 "MainWindow", 
      data = 0x805eac0, extradata = 0x0}}, findDialog = 0xbf91f688, 
  locationLabel = 0x805db19, formulaLabel = 0xb7f47958, curFile = {
    static null = {<No data fields>}, static shared_null = {ref = {value = 184}, 
      alloc = 0, size = 0, data = 0x806677a, clean = 0, simpletext = 0, 
      righttoleft = 0, asciiCache = 0, capacity = 0, reserved = 0, array = {0}}, 
    static shared_empty = {ref = {value = 1}, alloc = 0, size = 0, 
      data = 0xb757c00e, clean = 0, simpletext = 0, righttoleft = 0, 
      asciiCache = 0, capacity = 0, reserved = 0, array = {0}}, d = 0x8066768, 
    static codecForCStrings = 0x0}}
(gdb)