Changing Alert.PagerSendSubjectOnly property to True.

Hi everyone,

"Property PagerSendSubjectOnly is not available for AlertSystem '[SVRNAME]'. This property may not exist for this object, or may not be retrievable due to insufficient access rights.  (Microsoft.SqlServer.Smo)"

error while starting the SQL Server Agent 2012.

Please tell me how to change the above mentioned Property.

Thanks.