Error when converting migrated web app to Claims based

Hello,

We have a SharePoint 2010 farm & SharePoint 2013 farm, both are up & running.

all web application on SharePoint 2010 are classic authentication mode.

I'm trying to migrate a web app from 2010 to 2013 then convert it to claims based authentication using the following steps:

-Backup web app from SharePoint 2010
-Create a classic authentication mode web application in SharePoint 2013
-Delete the content database which was just created
-Validate the SharePoint 2010 content database can be upgraded
-Mount the database onto the new web application
-Reset and validate
-Then convert to claims mode.

I'm getting the following error when changing to claims mode:

PS C:\Windows\system32> Convert-SPWebApplication -Identity "http://webapp.local" -To Claims -RetainPermissions

Confirm
This operation will trigger user migration. It may take several hours for this process to complete depending on the
number of users. During this time the service will not be available. Do you want to continue?
[Y] Yes  [N] No  [S] Suspend  [?] Help (default is "Y"):

Confirm
This operation will add full rights to the web application for 'domain\spfarm'. Do you want to continue?
[Y] Yes  [N] No  [S] Suspend  [?] Help (default is "Y"):
WARNING: The conversion of web application and most of the users to Claims mode is completed. However, one or more
users could not be converted to Claims mode. Refer to the ULS logs for the details. For the troubleshooting tips refer
to the http://go.microsoft.com/fwlink/?LinkID=236943 article.
Convert-SPWebApplication : Access denied.  Only machine administrators are allowed to create administration service
job definitions of type: Microsoft.SharePoint.Administration.SPWebApplicationProvisioningJobDefinition,
Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c.
At line:1 char:1+ Convert-SPWebApplication -Identity "http://webapp.local" -To Claims -RetainPer ...+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ CategoryInfo          : InvalidData: (Microsoft.Share...tWebApplication:SpCmdletConvertWebApplication) [Convert-
   SPWebApplication], SecurityException+ FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SpCmdletConvertWebApplication

PS C:\Windows\system32> $webapp = Get-SPWebApplication -Identity "http://webapp.local/  "
PS C:\Windows\system32> $webapp.MigrateUsers($true)

Thanks, Shehatovich