It could be a code integrity issue. Even though the post in the first quote is over a year old there could be a code integrity problem with your copy. On the other hand the file may just be corrupted in a way that leads Avast to ID it.

AIS 6.0 has not identified it on my computer as a problem.

On this Desktop that I am typed this on there is one copy of mbamswissarmy.sys and it is located in c:\windows\SysWOW64\drivers.

Size is 38,224 bytes
Size on disk is 40,960

Created: 12/4/10
Modified: 12/20/10
Accessed: 12/22/10

Signature: Malwarebytes Corporation
File version: 1.50.1.0
original filename: mbamswissarmy.sys

I am getting this multiple times in my events:

Code integrity determined that the image hash of a file is not valid. The file could be corrupt due to unauthorized modification or the invalid hash could indicate a potential disk device error.

File Name: \Device\HarddiskVolume2\Windows\System32\drivers\mbamswissarmy.sys

Scandisk shows no errors on the drive and neither does the factory Diagnostic disk.

http://forums.malwarebytes.org/index.php?showtopic=6931

Code integrity is a measurement used in software testing. It measures the how high is the source code's quality when it is passed on to the QA, and is affected by how extensively the code was unit tested and integration tested. Code integrity is a combination of code coverage and software quality, and is usually achieved by unit testing your code to reach high code coverage.

With code integrity, the developer can be sure that his code is written correctly when passed on to QA. This is, in fact, the expected quality level of the code. Code integrity helps companies release better products, with fewer bugs, in a shorter time.

https://secure.wikimedia.org/wikipedia/en/wiki/Code_integrity