Escalation Level previously defined

Summary

Why do I get the Escalation Level previously defined error message

Content

Hi,

I am new to escalation rules so please make allowances if this is a stupid question....

I am trying to create a new rule to escalate Incidents with particular Product & Category combinations along the same lines as an existing rule.  When I attempt to set the escalation level on my new rule, I get the Escalation Level previously defined error message.  I clearly can't use the same escalation level twice but what is the reason for this?

I realise that I could enhance the existing rule to cover new P & C combinations but there are what I think are good reasons for not doing this.  However, if that is the only solution I will have to do so.