This indicates an attack attempt to exploit a Cross-Site Scripting vulnerability in D-Link DIR-866L.
The vulnerability is due to an error when the vulnerable software handles maliciously request to server. A remote attacker may be able to exploit this to execute arbitrary script code against a targeted site.
D-LINK DIR-866 REV-A 1.03b04
System Compromise: Remote attackers can execute arbitrary script code in the context of the affected site.
The router series is already at its End-Of-Life status, replace it with a new router of higher series.