get an error after updating the core properties

Hello,

I have just started using Open XML and I am trying to do something really simple to get and set the core properties of a document. I am using the following code

   public static void getProps(String fileName)
        {
            WordprocessingDocument document = null;
            try
            {
                document = WordprocessingDocument.Open(fileName, false);
                var docProps = document.PackageProperties;
                Console.WriteLine("Category " + docProps.Category);
                Console.WriteLine("ContentStatus " + docProps.ContentStatus);
                Console.WriteLine("ContentType " + docProps.ContentType);
                Console.WriteLine("Created " + docProps.Created);
                Console.WriteLine("Creator " + docProps.Creator);
                Console.WriteLine("Description " + docProps.Description);
                Console.WriteLine("Identifier " + docProps.Identifier);
                Console.WriteLine("Keywords " + docProps.Keywords);
                Console.WriteLine("Language " + docProps.Language);
                Console.WriteLine("LastModifiedBy " + docProps.LastModifiedBy);
                Console.WriteLine("LastPrinted " + docProps.LastPrinted);
                Console.WriteLine("Modified " + docProps.Modified);
                Console.WriteLine("Revision " + docProps.Revision);
                Console.WriteLine("Subject " + docProps.Subject);
                Console.WriteLine("Title " + docProps.Title);
                Console.WriteLine("Version " + docProps.Version);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                document.Close();
            }
        }

and

  public static void setProps(String fileName)
        {
            WordprocessingDocument document = null;
            try
            {
                document = WordprocessingDocument.Open(fileName, true);

                var docProps = document.PackageProperties;
                docProps.Category = "test21";
                docProps.ContentStatus = "test21";
                docProps.ContentType = "test21";
                docProps.Created = DateTime.Now;
                docProps.Creator = "test21";
                docProps.Description = "test21";
                docProps.Identifier = "test21";
                docProps.Keywords = "test21";
                docProps.Language = "test21";
                docProps.LastModifiedBy = "test21";
                docProps.LastPrinted = DateTime.Now;
                docProps.Modified = DateTime.Now;
                docProps.Revision = "test21";
                docProps.Subject = "test21";
                docProps.Title = "test21";
                docProps.Version = "test21";
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                document.Close();
            }
        }

after I call the setProps if I try to open the word document with word I will get an error that says

file xxx.docx cannot be opened because there is a problem with the contents

and then tells me that it has found some unreadable context and if I would like restore the document.

could someone tell me what I am doing wrong? and why this is happening.

cheers,

Ehsan