Adding second attachment to ticket fails?

Hi,

I have this C# code:

Code:

        private void CreateTicketAttachment(IEnumerable<TicketAttachmentInfo> attachments, Ticket ticket)
        {
            foreach (var attachment in attachments)
            {
                var ticketAttachmentRequest = new TicketAttachmentRequest()
                {
                    Contents = ConvertFileToBase64(attachment.TempFileName),
                    FileName = attachment.FileName,
                    TicketId = ticket.Id,
                    TicketPostId = ticket.Posts.Max(p => p.Id)
                };
                try
                {
                    if (ticketAttachmentRequest.IsValid(RequestTypes.Create))
                    {
                        _kayakoClient.Tickets.AddTicketAttachment(ticketAttachmentRequest);
                    }
                }
                catch (InvalidOperationException invOp)
                {
                    Message.Show(string.Format("AddTicketAttachment InvalidOperation: {0}", invOp.Message), MessageType.Error);
                }
                catch (ArgumentException argEx)
                {
                    Message.Show(string.Format("AddTicketAttachment ArgumentException: {0}", argEx.Message), MessageType.Error);
                }
                catch (Exception ex)
                {
                    Message.Show(string.Format("AddTicketAttachment exception: {0}", ex.Message), MessageType.Error);
                }
                finally
                {
                    File.Delete(attachment.TempFileName);
                }
            }
        }

Sometimes the attachment is added , but most of the times when adding I get this Exception:

{"There is an error in XML document (1, 2)."}
Looking at the inner exception I see this: {"<div xmlns=''> was not expected."}

BTW: I am using the C# wrapper library.

Any help would be appriciated.
Thanks!

I have been digging around and it seems to me that the problem occurs when the function of converting a file to a base64 string returns a string with slashes. This will proberly terminate the XML command to the REST api or something.
The base64 encoding works fine (tested this with the online tool [http://www.motobit.com/util/base64-decoder-encoder.asp]).
Could this be a bug in the C# wrapper or the REST api?