Mysql Forcing close of thread 946 user
This seems to be one of those errors that won't go away. In this case, it may be a case of human error.
First of all, here are a series of links with similar error messages on Shutdowns

http://www.webhostingtalk.com/showthread.php?t=518682
http://bugs.mysql.com/bug.php?id=7403
http://bugs.mysql.com/bug.php?id=48879
http://lists.mysql.com/mysql/206094
http://dev.mysql.com/doc/refman/5.6/en/error-log.html (See User Comments)
http://www.mail-archive.com/mysql@lists.mysql.com/msg12324.html

They all have seem to have one thing in common: MySQL for Windows.
It was claimed that Bug 7403 (the second link) was fixed and patch implemented July 14, 2005: http://lists.mysql.com/internals/27091
The versions of MySQL that this fix should be in 4.0, 5.0.40, 5.1.42. Looking in the error log you posted, I see you are using MySQL 5.1.67. Apparently, no one knows how to fix this issue or wants to (http://bugs.mysql.com/bug.php?id=7403) I also noted that the error messages indicate that you are using MySQL in Linux already.
I have three(3) suggestions that range from the most passive to the most aggressive...
SUGGESTION #1
Try setting log_warnings to 0, if you don't mind flying blind on warnings.
SUGGESTION #2
Upgrade to MySQL 5.6.11. Hopefully, there is should be more updates and bug fixes for this.
SUGGESTION #3
Move the Database to Linux. There should be more stability for this problem away on a better machine with the most updated kernel for the OS.
Give it a Try !!!
UPDATE 2013-04-30 11:20 EDT
Here is the fastest way to check for table corruption