Error Msg while exporting unbilled statement

When i try to export Unbilled statement as PDF i got this error msg. pls. advise

20.6.8: System.NullReferenceException: Object reference not set to an instance of an object
at #=zvJ_5AYSuRWx2h5D7IhHYx4y3GLT6G5GXmdMckEN9s5Js.#=zcBixJI$zetm1 (System.Char #=zL6f38OA=) [0x0002a] in :0
at #=zvJ_5AYSuRWx2h5D7IhHYx4y3GLT6G5GXmdMckEN9s5Js.#=zE4T4OQLYe4oC (System.Double #=zRXlxbB4=, System.Double& #=zobZWkgVS2BPAKsrBAg==) [0x000dc] in :0
at Apitron.PDF.Kit.FlowLayout.Content.TextBlock.Measure (Apitron.PDF.Kit.FixedLayout.Resources.ResourceManager resourceManager) [0x00119] in :0
at ManagerServer.Extensions.PdfConverter.GetMinWidth (Apitron.PDF.Kit.FlowLayout.ContentElement contentElement, System.Boolean nowrap, Apitron.PDF.Kit.FixedLayout.Resources.ResourceManager resourceManager) [0x0007e] in <6fccde4f6d63437d8de4e868406e029a>:0
at ManagerServer.Extensions.PdfConverter.GetMinWidth (Apitron.PDF.Kit.FlowLayout.ContentElement contentElement, System.Boolean nowrap, Apitron.PDF.Kit.FixedLayout.Resources.ResourceManager resourceManager) [0x000f4] in <6fccde4f6d63437d8de4e868406e029a>:0
at ManagerServer.Extensions.PdfConverter.GetMinWidth (Apitron.PDF.Kit.FlowLayout.ContentElement contentElement, System.Boolean nowrap, Apitron.PDF.Kit.FixedLayout.Resources.ResourceManager resourceManager) [0x000f4] in <6fccde4f6d63437d8de4e868406e029a>:0
at ManagerServer.Extensions.PdfConverter.GetMinWidth (Apitron.PDF.Kit.FlowLayout.ContentElement contentElement, System.Boolean nowrap, Apitron.PDF.Kit.FixedLayout.Resources.ResourceManager resourceManager) [0x000f4] in <6fccde4f6d63437d8de4e868406e029a>:0
at ManagerServer.Extensions.PdfConverter.Tr (AngleSharp.Dom.Html.IHtmlTableRowElement node, Apitron.PDF.Kit.Styles.Text.Font font, Apitron.PDF.Kit.FixedLayout.Resources.ResourceMana