Invalid Rectype Reference Key xxx : while inactivating Custom Segment.

Scenario

A user is a Getting Error: Invalid Rectype Reference Key xxx on saving Custom Segment.

Solution

1. Navigate to Customization > List , Records, & Fields > Custom Segment 
2. Click Edit on the Custom Segment for which you are getting this Error.
3. Click Application & Sourcing Subtab > Other Record Types
4. Revenue Recognition Treatment : Remove Checkmark
5. Recognition Treatment Rule : Remove Checkmark
6. On Filters By field, remove selected fields.
7. Click Save