database error mail from vbulletin forum

[sowmya002]

Hi,

We are getting mails of the below kind in from our vbulletin forum. Though not so frequent these kinds of mails keep coming from the forum. As you can see from the message pasted below the version is latest. Please let me know how to get rid of these.

Database error in vBulletin 5.1.5:

Invalid SQL:
SELECT * FROM routenew
WHERE `prefix` IN ('forum/xxxxx','forum/xxxx','forum');

MySQL Error : Illegal mix of collations for operation ' IN '
Error Number : 1271
Request Date : Thursday, February 5th 2015 @ 05:56:07 AM
Error Date : Thursday, February 5th 2015 @ 05:56:08 AM
Script : http://
Referrer :
IP Address : 207.46.13.65
Username : Guest
Classname : vB_Database_MySQLi
MySQL Version :

Thanks!
Sowmya