Hi, I'm pretty new to Salesforce (had this job about 3 weeks) and I'm trying to set up a validation rule that prevents one particular user from creating an event anywhere but in opportunities.
Here's the logic on the validation rule:

CreatedBy.Id = "00530000002EKrz" 
&& 
NOT(LEFT(WhatId,3) = "006")

Now, when I try to create an event while logged in as this user, I get the following error message:

Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger Event_AfterInsert caused an unexpected exception, contact your administrator:
Event_AfterInsert: execution of AfterInsert caused by: System.DmlException: Update failed. First exception on row 0 with id 00UV0000001jJghMAE; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, This event must be associated with an opportunity.: []: Trigger.Event_AfterInsert: line 12, column 1

So it's having some kind of problem with 'Event_AfterInsert'. That's this:
 

trigger Event_AfterInsert on Event (after insert)
{
	For (Event e : trigger.new)
    {
        For (Account a : [Select Id, Region__c from Account where Id = :e.AccountId])
	    {
	        // Update the event record
			Event[] ev = [select id, Region__c from Event where id = :e.Id];
			ev[0].Region__c = a.Region__c;
			update ev[0];
	    }
    }
}

But I have no idea where to go from here.  The 'This event must be associated with an opportunity' part of the error message is exactly what I put as my validation rule's error message, which is also confusing me.

Any help would be greatly appreciated.
Thank you!