unble to change admin email address

[wildwilla]

When i try to change the admin emaill address(Server > Administrator information)i get the following error

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Top > Virtuozzo > Resources > Extended
Service Unavailable Active Tasks
Service is not available now, probably your Plesk is misconfigured.
Contact Your provider for details.

Internal Plesk error occurred: dnsmng::restart() failed: dnsmng failed: dnsmng: Empty fields 'host' or 'opt' in PTR record
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Any idea how to resolve this?