This indicates an attack attempt to exploit an Information Disclosure vulnerability in Microsoft Excel.
This vulnerability is due to an error when the affected application handles maliciously crafted file. A remote attacker may be able to exploit this to gain access to sensitive information, via a crafted file.
Microsoft Excel 2007
Microsoft Excel 2010
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.