Harrop had been in charge at the Iron since 2022 - leading the club to consecutive play-off campaigns, winning last season's National League South Promotion Final at Worthing.
He leaves the club hovering above the bottom four following back-to-back 3-1 defeats, their latest coming at the hands of Maidenhead United on Tuesday night.
Chairman Lee Harding made the following statement on social media: "We have been talking with Angelo since the start of the season and the Board have decided it is time for a change to safeguard the Club's future.
"We would like to thank Angelo for his efforts over the past two and a half years at the Club. We have achieved much together on and off the field and wish him all the very best in the future.
"We then spoke with both Justin Moseley and senior players after the game, who have all agreed to help the Club going forward. All of us are now focused on turning our fortunes around with training this week and our game against Gateshead on Saturday."