Follow below steps:
1) Start Registry Editor.(run regedit.exe)
2) If you are prompted for an administrator password or for a confirmation, type the password, or click Continue.
3) Locate and then click the following registry subkey:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security
4) On the Edit menu, point to New, and then click DWORD Value.
5) Type ExtensionHardening, and then press ENTER.
6) Right-click ExtensionHardening, and then click Modify.
7) In the Value data box, type 0, and then click OK.
You are done.
:doh:
[Another workaround]:
ClosedXML - The easy way to OpenXML[
^]
[Update]:
Excel 2007 Extension Warning On Opening Excel Workbook from a Web Site[
^]
Regards.. :laugh: