For adding attachments in list and showing all attachments in next task, I have followed this link (collect task attachments in list item and show all attachments in next task ).
When I use actions of collecting attachments in list (AddAttachment-call web service) action gives me error : "The workflow could not update the item, possibly because one or more columns for the item require a different type of information".
I don't get this error while using first time. whole actions work properly but using it for second time causes error in AddAttachment action.
Please give your suggestions