I cannot figure out for the life of me why I am getting the CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, Glen_Task_Chatter: execution AfterInsert error

test code:

public with sharing class test_Glen_Task_Chatter {

    /*
    *    Test the ChatterActivity trigger which inserts chatter feed posts whenever a task is inserted on the parent object
    */
    public static testMethod void testChatterActivity() {
        //create the test account
        
        User u1 = [select id from User where alias='gbrad'];
        
//Run As U1  
    
        System.RunAs(u1){
        
        Account a = new Account(name='Test Account', Type='Law Firm', Industry='Agriculture', BillingCity='Indianapolis', BillingCountry='USA');
        insert a;
        
        Contact c = new Contact(LastName='Test Account', AccountId=a.id, Title='test', Email='g@g.com', LeadSource='Adwords');
        insert c;

        //create a task on that account
        Task t = new Task(Subject='Subject', Contact_Outreach__c='Log A Phone Meeting',WhoId=c.Id,WhatId=a.id,Ownerid=u1.id);
        insert t;
        
        //Event e = new Event (Subject='Subject', Related_Services__c='Consulting', DurationInMinutes=30, ActivityDateTime=datetime.now());
        //insert e;
        
        }
    }
}

Actual Trigger:

trigger Glen_Task_Chatter on Task (after insert, after update) {

    if(UserInfo.getName()!='Eloqua Marketing'){
    
        List<FeedItem> feedItems = new List<FeedItem>();
    //We want to show the User name as assignedTo. The only way to get to that is by querying the user table.
        Set<ID> ownerIds = new Set<ID>();
        
        for (Task t : Trigger.new) {
            ownerIds.add(t.ownerId);
        }
        Map<ID,User> userMap = new Map<ID,User>([SELECT ID, Name FROM User WHERE ID IN :ownerIds]); //This is our user map
    
    
    
        for (Task c: Trigger.new) {
                
                    FeedItem fitem = new FeedItem();
                    fitem.type = 'LinkPost';
            		if (c.Accountid != null)
                    	fitem.ParentId = c.Accountid;
                    fitem.LinkUrl = '/' + c.id; //This is the url to take the user to the activity
                    fitem.Title = 'View';  //This is the title that displays for the LinkUrl
        
                    //Get the user by checking the userMap we created earlier
                    User assignedTo = userMap.get(c.ownerId);
        
                    fitem.Body = ((Trigger.isInsert) ? 'New' : 'Updated') + ' Task - ' + c.Subject +': ' + c.Contact_Outreach__c + '\n  ' + c.Description.substring(0,50); //+ c.Who.Name;
                    
                    if (c.AccountId !=null)
                        feedItems.add(fitem);
                
        //}
    
    
        //Save the FeedItems all at once.
        if (feedItems.size() > 0) {
            Database.insert(feedItems,false); //notice the false value. This will allow some to fail if Chatter isn't available on that object
        }
    
    
        
    
        }
        
        
        
        
        
    }

    
    
    
}