I had worked at my previous employer for 13 years as a Staff Analyst/Developer. A new manager and I did not see eye to eye on many recent projects as she was a professional manager and non-technical. I was called into an office on Monday and told in a meeting with her, my VP and an HR rep that I was being terminated but that due to my long years of service I would be given the opportunity to resign. I felt punched in the stomach and did not know what more to say other than to agree to resign. I even found out later that my manager went around saying that I had resigned unexpectedly.
While that scenario is unusual I am less concerned with the past and more concerned with how I get over it and move on with a new employer. What should I say during interviews as to why I 'resigned unexpectedly'? How do I explain when they call my previous employer that I am ineligible for rehire? This is in the US, specifically Colorado.