Running Vista Enterprise, Office 2007

Excel 2007 - sharing a workbook
file saved to a network drive.
File worked with no problems in 2003 on XP

Users open file make changes and try to save - receives errors:
either - File is Locked
or
"The document was saved successfully, but Excel cannot re-open it because of
a sharing violation. Please close the document and try to open it again."

Changes done by current or other users are not getting saved
Even though it says it's been saved if reopen changes are not there.