I found a problem, I put on one form win toolbar manager, and win explorer bar. I activated that form (Form a)  from another form (Form b), so when i push button on Form b, I create Form a. First time when it shows up, it's ok, I turn it off (just Form a, Form b stays on), and press the button again in Form b, and it again shows Form a fine, but when I click button for the third time, it gives mi this error

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************** Exception Text **************
System.ArgumentException: Parameter is not valid.
   at System.Drawing.Graphics.GetHdc()
   at Infragistics.Win.FormattedLinkLabel.PositionElementsCache.MeasureTextGDIOrThemed(String text, Font font, TextFormatFlags textFormatFlags)
   at Infragistics.Win.FormattedLinkLabel.PositionElementsCache.MeasureCharacterRangesGDI(String text, Font font, TextFormatFlags textFormatFlags, CharacterRange[] ranges)
   at Infragistics.Win.FormattedLinkLabel.PositionElementsCache.ReMeasureParts(String text, Int32[] parts, Single[] widths, Int32 partStartIndex, Int32 partEndIndex, Font font, Single& lineHeight)
   at Infragistics.Win.FormattedLinkLabel.PositionElementsCache.MeasureParts(String text, Int32[] parts, Font font, Single& lineHeight)
   at Infragistics.Win.FormattedLinkLabel.NodeText.TextLayoutInfo.Measure(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeText.PositionSelf(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBase.PositionHelper(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBase.Position(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBase.PositionChildNodes(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBlock.PositionChildNodes(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBase.PositionHelper(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBase.Position(PositionElementsInfo& info)
   at Infragistics.Win.FormattedLinkLabel.NodeBase.CalcSize(IFormattedLinkLabelOwner owner, Graphics graphics, Int32 maxWidth)
   at Infragistics.Win.FormattedLinkLabel.ParsedFormattedTextValue.CalcSize(Graphics graphics, Font baseFont, AppearanceData& defaultAppearance, Int32 widthConstraint, DefaultableBoolean wrapText, GdiDrawStringFlags gdiDrawStringFlags)
   at Infragistics.Win.UltraWinToolbars.Ribbon.RibbonMetrics.CalculateCaptionAreaHeight()
   at Infragistics.Win.UltraWinToolbars.Ribbon.RibbonMetrics.get_CaptionAreaHeight()
   at Infragistics.Win.UltraWinToolbars.UltraToolbarsDockArea.CalculateGlassRect()
   at Infragistics.Win.UltraWinToolbars.UltraToolbarsManager.ExtendGlassIntoRibbon(IntPtr handle)
   at Infragistics.Win.UltraWinToolbars.UltraToolbarsManager.RefreshGlass()
   at Infragistics.Win.UltraWinToolbars.Ribbon.RibbonMetrics.Dirty(RibbonMetricsFlags flags)
   at Infragistics.Win.UltraWinToolbars.Ribbon.OnRibbonContainerResized()
   at Infragistics.Win.UltraWinToolbars.UltraToolbarsDockArea.RefreshDockAreaSize(Size& currentSize)
   at Infragistics.Win.UltraWinToolbars.UltraToolbarsDockArea.SetBoundsCore(Int32 x, Int32 y, Int32 width, Int32 height, BoundsSpecified specified)
   at System.Windows.Forms.Control.System.Windows.Forms.Layout.IArrangedElement.SetBounds(Rectangle bounds, BoundsSpecified specified)
   at System.Windows.Forms.Layout.DefaultLayout.xLayoutDockedControl(IArrangedElement element, Rectangle newElementBounds, Boolean measureOnly, Size& preferredSize, Rectangle& remainingBounds)
   at System.Windows.Forms.Layout.DefaultLayout.LayoutDockedControls(IArrangedElement container, Boolean measureOnly)
   at System.Windows.Forms.Layout.DefaultLayout.xLayout(IArrangedElement container, Boolean measureOnly, Size& preferredSize)
   at System.Windows.Forms.Layout.DefaultLayout.LayoutCore(IArrangedElement container, LayoutEventArgs args)
   at System.Windows.Forms.Layout.LayoutEngine.Layout(Object container, LayoutEventArgs layoutEventArgs)
   at System.Windows.Forms.Control.OnLayout(LayoutEventArgs levent)
   at System.Windows.Forms.ScrollableControl.OnLayout(LayoutEventArgs levent)
   at System.Windows.Forms.Form.OnLayout(LayoutEventArgs levent)
   at System.Windows.Forms.Control.PerformLayout(LayoutEventArgs args)
   at System.Windows.Forms.Control.System.Windows.Forms.Layout.IArrangedElement.PerformLayout(IArrangedElement affectedElement, String affectedProperty)
   at System.Windows.Forms.Layout.LayoutTransaction.DoLayout(IArrangedElement elementToLayout, IArrangedElement elementCausingLayout, String property)
   at System.Windows.Forms.Control.OnResize(EventArgs e)
   at System.Windows.Forms.Form.OnResize(EventArgs e)
   at System.Windows.Forms.Control.OnSizeChanged(EventArgs e)
   at System.Windows.Forms.Control.UpdateBounds(Int32 x, Int32 y, Int32 width, Int32 height, Int32 clientWidth, Int32 clientHeight)
   at System.Windows.Forms.Control.UpdateBounds()
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.ContainerControl.WndProc(Message& m)
   at System.Windows.Forms.Form.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

And it only happens with the combination of ultra toolbar manager, set to show ribbon, and ultra explorer bar. If I set toolbar manager FormDisplayStyle to Standard, everything is fine. And also, the problem doesn't show up always, it sometimes does, and sometimes doesn't. Very strange...