Itext sharp 5.5.13 random errors like "The page 929 was requested but the document has only 928 pages." - itext

Question

maybe one of you, had the same problem and could help me. We have got random errors during merge ducuments from code below:
public static byte[] MergePdfFiles(List<byte[]> pdfFiles, object lockObject)
{
lock (lockObject)
{
using (MemoryStream ms = new MemoryStream())
{
using (Document doc = new Document())
{
//you also see here that I did not put PdfSmartCopy into a using block. This is because the Document implicitly closes the PdfSmartCopy when it is disposed
PdfSmartCopy copy = new PdfSmartCopy(doc, ms) {CloseStream = false};
doc.Open();
//Loop through each byte array
foreach (var pdfByte in pdfFiles)
{
using (PdfReader pReader = new PdfReader(pdfByte))
{
for (int i = 0; i < pReader.NumberOfPages; i++)
{
PdfImportedPage pdfMerger = copy.GetImportedPage(pReader, i + 1);
copy.AddPage(pdfMerger);
}
copy.FreeReader(pReader);
}
}
}
//Return just before disposing
return ms.ToArray();
}
}
}
This errors occured during close document:
at iTextSharp.text.pdf.PdfWriter.Close()
at iTextSharp.text.pdf.PdfCopy.Close()
at iTextSharp.text.pdf.PdfDocument.Close()
at iTextSharp.text.Document.Close()
at iTextSharp.text.Document.Dispose()
at PdfTools.PdfHelperTools.MergePdfFiles(List`1 pdfFiles, Object lockObject) in C:\src\businessLogic-lib\PdfTools\PdfHelperTools.cs:line 154
at Lawsuit.LettersWithAttachments.LettersWithAttachmentsPrint.MakeControlPrint(Int32 controlPrintId) in C:\src\businessLogic-lib\Lawsuit.LettersWithAttachments\LettersWithAttachmentsPrint.cs:line 611
at Api.BusinessLayer.Manager.AttachmentManager.MakeControlPrint(Int32 controlPrintId) in C:\src\mService-RestService\Api.BusinessLayer\Manager\AttachmentManager.cs:line 94
at Services.Api.Controllers.LawsuitLegalController.PrintAttachmentLegalControlPrint(Int32 controlPrintId) in C:\src\LegalService-RestService\LegalService\Controllers\LawsuitLegalController.cs:line 213
at lambda_method(Closure , Object , Object[] )
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)
at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__0.MoveNext()
Errors such as:
The page 929 was requested but the document has only 928 pages.
The page 693 was requested but the document has only 692 pages.
The page 1090 was requested but the document has only 1089 pages.