I encountered the following message when trying to change a password for a managed account:
Error deploying administration application pool credentials. Another deployment may be active. An object of the type Microsoft.SharePoint.Administration.SPAdminAppPoolCredentialDeploymentJobDefinition named "job-admin-apppool-change" already exists under the parent Microsoft.SharePoint.Administration.SPTimerService named "SPTimerV4". Rename your object or delete the existing object.
The error message is self explanatory - Rename your object or delete the existing object. I choose the latter. Powershell to the rescue.
$job = Get-SPTimerJob -Identity "job-admin-apppool-change"
Reset the password and all should be good.