Enhanced On-Access Anti-Malware Protection stopped working

Hello everyone

My OS is Windows Vista Premium Home Edition 32 Bits. I'm working with this
OS since I have bought my recent PC, about one year ago. Besides a good
antivirus and firewall always updated and activated, my Windows is also
updated. Same thing to Windows Defender.
About 15-20 days from now, when I log to my PC as an administrator, it
appears, a few minutes later, a message in my desktop saying that Enhanced
On-Access Anti-Malware Protection stopped working. It gives me two options:
close the dialog box or look at the Internet for solutions. I don't know what
this is, so I choose to close the box.

Can you help out with this?
What kind of problem is this and what might have caused it?
Here's more details regarding this problem:


Name of the Event of the problem: APPCRASH
Aplication name: AVENGINE.EXE
Aplication version: 2.1.29.0
Carimbo de Data/Hora da Aplicação: 468e2cc5
Name of the Model with fails: pskscs.dll
Version of the failing model: 1.4.3.30
Carimbo de Data/Hora do Módulo com Falhas: 469ddbdb
Exception Code: c0000005
Desvio de Excepção: 00026f48
Versão do SO: 6.0.6000.2.0.0.768.3
ID de Região: 2070
Informações Adicionais 1: a743
Informações Adicionais 2: b4243b2b695c85b0cfbb26ee26cb0b3e
Informações Adicionais 3: c7fa
Informações Adicionais 4: 9b83326186aec212c406c4ddca14e06b

My OS is in Portuguese (European); some of the expressions I wasn't able to
find a appropriate translaction to portuguese. I'm sorry...

And another detail: this only happens when I'm logged as an administrator.
In the other user accounts this does not happen.

I'm sorry for my Giant post...
Thanks in advance

Enhanced On-Access Anti-Malware Protection stopped working