When running a workflow that copies a file to a specified library, the following error might occur intermittently:
The workflow could not update the item, possibly because one or more columns for the item require a different type of information.
Review the workflow design. Where the workflow is attempting to update the list item, ensure that the datatype of the information being posted to the SharePoint list is the same as the column's datatype.
The workflow is attempting to post a value back to the SharePoint list prior to that value being set by the workflow. Place a Commit Pending Changes action or a Pause action prior to the list item update to prevent the workflow from attempting to post a NULL value to the SharePoint list.