The workbook you are saving probably has a linked formula to another
workbook that has not been saved yet (ie book1 ot book2 or something) Excel
is warning you because you will need to update those links (in the workbook
you are saving)to the filename that you save the book1 workbook to.
Save "filename" with reference to unsaved documents
The interrupted save writes to an error log file at C:\Documents and Settings\"your user directory"\Local Settings\Temp The file name begins with "Error" and may contain a number. The error file contains the information that was unreadable or otherwise scrambled on the attempted save. If your original file is relatively intact and you want to remove the nagging message, delete this error file and the "reference to unsaved documents will go away.
This works if there are no links in the spreadsheet that are recoverable.
I found the solution to "Save xxxx with reference to unsaved documents" issue
1. Click on the Data tab of the worksheet giving you the issue
2. Click on Connections
3. The unknown workbook that is currently connected or linked to your worksheet will be listed here
4. Highlight the worksheet and remove
5. Attempt to save your worksheet again.
This is per Excel 2016 and worked for me. Good luck.