Accounts that are functional accounts for this or other systems cannot be deleted. The account management screen will show in brackets if the account is a functional account - (Functional Account for this System) and/or (Domain Functional Account for other systems)
Functional Account for this System
On the "Connection" tab use a different functional account, or disable PPM by unticking "Enable Automatic Password Management?" on the "Information tab" The account can then be deleted.
Domain Functional Account for other systems
Select "Current Status", this will show where the account is being used for a either PPM functional account or PSM.