This indicates an attack attempt to exploit a Remote Code Execution vulnerability in Microsoft Office.
The vulnerability is due to an improper search path in the application leading to insecure loading of a dll file. An attacker can exploit this by tricking an unsuspecting user into opening a file from a directory and execute arbitrary code within the context of the application.
Microsoft Excel 2007 Service Pack 3
Microsoft Excel 2010 Service Pack 2 (32-bit editions)
Microsoft Excel 2010 Service Pack 2 (64-bit editions)
Microsoft Excel Viewer 2007 Service Pack 3
Microsoft Office Compatibility Pack Service Pack 3
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.