We have an intermittent error where a workflow attempts to edit an existing Excel workbook using excelservice.asmx OpenWorkbookForEditing. The error says "Someone else has the workbook checked out or opened in Excel; it can't be edited in the browser", but we have made absolutely sure that it is neither checked out nor open anywhere and still get this error. I don't think the Call Web Service action configuration is the problem since it does work for other items, but for what it's worth here it is:
The variable slt_Filename does not contain "?Web=1".