There are a number of standard Salesforce features that can prevent a Salesforce User from being deactivated.
You cannot deactivate a Salesforce user if they are…
- the Web-to-Lead Default Creator
- allocated leads using Lead Assignment Rules
- specified in Lead Auto-Response Rules
- specified in a Lead Process
- the Default Case Creator
- an Automated Case Owner
- specified in Case Assignment Rules
- specified in Case Auto-Response Rules
- designated as a record owner in a workflow or approval process
- assigned tasks in a workflow or approval process
- sent emails as part of a workflow or approval process
- already in an approval process or designated as an approver or delegated approver
- the default workflow user
- the selected User in a custom hierarchy field
Any attempt by Skuser to deactivate a Salesforce User that is used in one or more of the above scenarios will fail.
Additionally, Skuser will not attempt to deactivate a user if
- Do Not Deactivate checkbox is checked on User record
- there is not a Pool Member record associated with the User
- there is a Pool Member record associated with the user, but the Pool Member Allocation Status is not ‘Allocate’

