I know this is an old thread, however I am experiencing exactly the same thing.
I have a single workbook, in Excel 2003 which the:
Tools=>Share Workbooks....
is greyed out. It's relevant only to this specific workbook. I inherited the Workbook from a colleague at work. It's pretty big, about 5 Mbytes. It had a list in it, which I converted to a range.
I saved the Workbook, closed it, killed Excel, re-opened the workbook, and no joy.
Any suggestions would be greatly appreciated.
Thanks in advance.