You have a requirement to set up Number Ranges for Employees and Service Agents and System throws an Error "Difference between total length 0004 and prefix length 1 must exceed 4" when you are trying to Change the Total Length from one value to another.
Reproducing the Issue
1) Go to the Business Configuration Work Center
2) Select Implementation Projects
3) Click Open Activity List and Search for "Number Ranges for Employees and Service Agents"
4) Change the Total Length from a Higher Value to 0004 or less, when there is a Prefix(Static) of Length 1
This is an expected system behaviour.
As it is required that the sequential number in employee/service agent ID should be at least 4 digits.
So Total Length should be at least 0005 if you define 1-letter Prefix eg: 'S' and at least 0006 if you define 2-letter Prefix eg: 'SS' and so on.
Number Ranges for Employees and Service Agents, Total Length , KBA , AP-RC-NR , Number Ranges (SAP Business ByDesign) , How To