How do I resolve this error that I keep receiving emails for?

Hi Tashiera - that error is NPSP's nightly job (runs around 3am) choking on an Opportunity owned by a deactivated user. 005C000000AYRGD is a User Id (the '005' prefix means User) - you cannot find 'feroze' because they are inactive. To see them, go to Setup - Users and switch the list view from 'Active Users' to 'All Users'. 

Two things to fix, and your message ('...as owner of opportunity') points to the first: 

1. Reassign the records they own. Build a report or list view of Opportunities where Owner = that inactive user, then reassign them to an active user (Setup - Mass Transfer Records, or Data Loader). Salesforce blocks operations on records owned by inactive users, which is exactly what the nightly rollup hits - once none are owned by that user, the 3am error stops. 

2. While you are there, check the NPSP scheduled jobs' 'Submitted By'. If a default NPSP job was scheduled by that same inactive user, reschedule it: NPSP Settings - Bulk Data Processes - Batch Process Settings (recreating the default jobs runs them as an active user). 

The emails go to whoever is set as the Error Notification recipient in NPSP Settings; they stop once the ownership (and any inactive-submitted job) is cleaned up. 

If this helps, please mark it as the Best Answer so it helps the next person - thanks :)