Repeated error from same Ip

[Mecha Dude]

YaBB SE Version: 1.5.4
PHP Version: 4.3.2
MySQL Version: 4.0.x
Server Platform: Unix, Linux, or BSD
Link to Forum: http://www.knightofxentar.com

Problem Description:
For the past several days, someone not from my forum has been generating about 2 pages in errors.
The error title is: "Session check failure. Please try again."
What they where trying to do was this:/yabbse/index.php?board=5;action=post;threadid=106;quote=683;title=Post+reply;start=0;sesc=04197198c4809094335b99fd4d0a0b0d

Now the info is diffrent from each error, but it's all on the same board in my forum.

Should I be worried?  Are they just having really bad luck?

[Douglas]

Chances are that it's a robot/spider trying to index your site.  Have you looked the IP address up with Arin yet?

[Mecha Dude]

This looks rather strange  I've never seen this little data before.

AT&T WorldNet Services ATT (NET-12-0-0-0-1)
                                 12.0.0.0 - 12.255.255.255
NAMEPROTECT.COM NAMEPROT75-209-192 (NET-12-148-209-192-1)
                                 12.148.209.192 - 12.148.209.255