So the problem is that the agent handler is using credentials to connect to the SQL server that have been disabled since de ePO admin left the company.
If you want to change these credentials and use the same as ePO is using then try this: https://kc.mcafee.com/corporate/index?page=content&id=KB75333
If you need different SQL credentials (for example if your agent handler is on dmz and needs to use SQL credentials instead of Windows credentials) then you should run the agent handler setup again and install with new credentials
The credential use to connect to ePO database is still intact and being used by the ePO server. Maybe when the ePO admin left the company and his account get terminated, all the settings he did during the first install on the Agent Handler is disregarded including the database credential.
What I did here is I added these credentials on the administrator group (same settings with the ePO server) and follow the KB article you shared and it works and communication problem restrore to its normal state and I can start the Agent Handler Event Parser service.
Thanks for your help, really appreciate this.
Something I just wanted to note here, since I didn't know about it when I adopted my McAfee environment (after the previous admin abruptly quit) and then ran into problems:
Do not delete the previous admin's account from the console right away!
A wonderful "feature" of ePO is that when you delete the user account, it also deletes all of the tasks, policies, etc. which are associated with that account. The easy way around this is to 'edit' the tasks, policies, queries, etc. that you want to keep (which the previous admin made), don't make any changes, but then 'save' whatever it is you're looking at. This will then reassociate that thing with the user account you're using and will be safe from being deleted whenever you get around to deleting the other account.