Index was outside the bounds of the array.

What does this error mean and what are the possible causes?
Thanks

---------------- Exception(s) ----------------

Message: Exception of type 'System.Web.HttpUnhandledException' was thrown.

Inner Exception
----------------------------------------------

Message: Index was outside the bounds of the array.
Source: DynamicPDF.Merger.Server
Stack Trace: at zz93.u.e(Stream A_0)
at zz93.u..ctor(PdfDocument A_0, aw A_1)
at ceTe.DynamicPDF.Merger.PdfDocument.c()
at ceTe.DynamicPDF.Merger.PdfDocument..ctor(ax A_0, String A_1)
at ceTe.DynamicPDF.Merger.PdfDocument..ctor(String filePath)
at UltraITSolutions.Framework.Core.AgentReportDocument.Open()
at UltraITSolutions.Framework.Core.AgentReportDocument..ctor(String filepath)
at MySiteDB.UI.SaleProperty.Reports.ViewReport.Page_Load(Object sender, EventArgs e)
at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
at System.Web.UI.Control.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Hello,

Are you using any existing PDF documents? If so please send over the PDF document and the code you are using to merge the PDF to our Support Team so that they can look into it further.

Thanks,
ceTe Software Support Team.

The error seems to be caused by a corrupt PDF file, either by a problem with LiveCycle or the FP software.
I have opened the document and resaved it using a different computer and then uploaded it. It works fine now.