I am having a similar problem, so I'm anxious to see any solution or
explanation. See my post "Share Workbook command is not available
(greyed out)" from May 23, 2006.
For those suggesting solutions, the following are NOT factors:
*Opened (Readonly) is not the case
*No write access to the shared drive is not the case
*Prevented (at least knowingly) by the document's creator is not the
case
*Not being created by the person attempting to turn on sharing is not a
factor. This is not a restriction on other documents not created by the
person attempting to invoke sharing.
It appears that there is some feature used in this spreadsheet which
then renders it unsharable, so the "Share Workbook" feature is turned
off and not available to be selected. Otherwise, we are doing nothing
different from other previously shared workbooks of a similar nature.
The only factors different in my case is that there are some more
complex features in use (Lists, functions, etc.) than in some other
shared workbooks.
Any solution to this question would be most appreciated!