You cannot add digital signature to shared workbooks

When you attempt to add a valid digital signature to a workbook, the signature is not shown in the Digital Signature dialog box and no error message is displayed.

This problem occurs when the workbook is shared.

NOTE: This problem only affects digital signatures that are applied to a workbook. It does not affect digital signatures that are applied to the workbook's Visual Basic project.

To work around this issue, remove the workbook from shared use. To do this, follow these steps:

1. In Microsoft Office Excel 2003 or in Microsoft Excel 2002, click Share Workbook on the Tools menu.
   
   In Microsoft Office Excel 2007, click Share Workbook in the Changes group on the Review tab.
2. On the Editing tab, click to clear the Allows changes by more that one user at the same time check box.
3. Click OK.
4. If you are prompted, click Yes to save the file.

To add a digital signature to the workbook, follow these steps.

In Excel 2003 or in Excel 2002

1. On the File menu, click Save. Provide the file name and path, and click Save.
2. On the Tools menu, click Options.
3. In the Options dialog box, click the Security tab.
4. Click Digital Signatures.
5. In the Digital Signature dialog box, click Add.
6. Select the digital certificate that you want to use to sign the workbook, and then click OK.
7. Click OK to close both the Digital Signature dialog box and the Options dialog box.

In Excel 2007

1. Click the Microsoft Office Button, and then click Save.
2. Provide the file name and path, and click Save.
3. Click the Microsoft Office Button, point to Prepare, and then click Add a Digital Signature.
4. In the Sign dialog box, click Change.
5. In the Select Certificate dialog box, select the digital certificate that you want to use to sign the workbook, and then click OK.
6. In the Sign dialog box, click Sign.

For more information about digital signatures, press F1 to open Excel Help, type digital signatures in the Search box, and then click Search to view the topics that are returned.

For more information about the limitations of shared workbooks, press F1 to open Excel Help, type features that are unavailable in shared workbooks in the Search box, and then click Search to view the topic.