Error message: Specified cast is not valid.

Url: http://zafmarkt.com/skin.aspx?lang=en&itemtype=ProductCategory&itemalias=ergaleia-xeiros-penses-0098be63&action=view&000003F3=009A44FD‡009A451D‡009A4514‡009A4500‡009A450C‡009A4502‡009A4503‡009A44FF‡009A4512&splitter_products_offset=0
Message: Specified cast is not valid.
   at Ecommerce.Product.get_UserPrice() in C:\Bone\Ecommerce\src\DBItems\Product\Product.cs:line 439
   at Ecommerce.Product.get_PriceBeforeDiscount() in C:\Bone\Ecommerce\src\DBItems\Product\Product.cs:line 460
   at ASP.tpl_tiles_product_tile_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\inetpub\wwwroot\tpl\tiles\Product.tile.ascx:line 70
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at Bone.BONE.LoadControl(String virtual_path, DBItem item, Boolean cache, Boolean hide_debug_sign, Object[] objects, String default_if_file_no_exists) in C:\Bone\Bone\src\BONE.cs:line 0
   at Bone.BONE.LoadControl(String virtual_path, DBItem item, Boolean cache, Object[] objects) in C:\Bone\Bone\src\BONE.cs:line 2653
   at Bone.DBItem.TileWithInfo(Object[] objects) in C:\Bone\Bone\src\EngineDB\DBItem.cs:line 1317
   at Bone.DBItem.get_Tile() in C:\Bone\Bone\src\EngineDB\DBItem.cs:line 1342
   at Bone.TilesetControl.<>c.b__33_0(Object x) in C:\Bone\Bone\src\EngineUI\UIControls\TilesetControl.cs:line 188
   at Bone.TilesetControl.Render(TextWriter w) in C:\Bone\Bone\src\EngineUI\UIControls\TilesetControl.cs:line 216
   at Bone.UIControl.ToString() in C:\Bone\Bone\src\EngineUI\_Control.cs:line 30
   at System.IO.TextWriter.Write(Object value)
   at ASP.tpl_productcategory_view_tpl_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\e22c2559\92c7e946\App_Web_gxq444q0.4.cs:line 0
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at Bone.ActionView.Render(TextWriter w) in C:\Bone\Bone\src\Actions\DBActions\ActionView.cs:line 137
   at Bone.Action.RenderContent(TextWriter w) in C:\Bone\Bone\src\Actions\_Action.cs:line 355
   at Bone.Action.ToString() in C:\Bone\Bone\src\Actions\_Action.cs:line 516
   at Bone.Base.get_Content() in C:\Bone\Bone\src\Classes\Base.cs:line 80
   at ASP.skin_aspx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\inetpub\wwwroot\skin.aspx:line 301
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Page.Render(HtmlTextWriter writer)
   at Bone.Asp.RenderSkin(TextWriter w) in C:\Bone\Bone\src\Classes\Asp.cs:line 71
   at Bone.ModalAction.RenderPage(TextWriter w) in C:\Bone\Bone\src\Actions\Modal.cs:line 81
   at Bone.Asp.Render(HtmlTextWriter w) in C:\Bone\Bone\src\Classes\Asp.cs:line 82
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)