This indicates an attack attempt to exploit a Directory Traversal vulnerability in Microsoft Internet Information Services.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. As a result, a remote attacker can gain unauthorized access to sensitive information or execute codes that are already on the server.
Microsoft IIS 4.0
Microsoft IIS 5.0
System Compromise: Remote attackers can gain control of vulnerable systems
Refer to the vendor's website for suggested workaround.