2013 – The base type ‘Microsoft.Office.Server.Search.Internal.UI.SearchAdministration’ is not allowed for this page

Search Service application worked fine before but after some days when i open search service application from central admin below error appears.

The base type ‘Microsoft.Office.Server.Search.Internal.UI.SearchAdministration’ is not allowed for this page. The type Microsoft.Office.Server.Search.Internal.UI.SearchAdministration, Microsoft.Office.Server.Search, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c could not be found or it is not registered as safe.

what cause this issue occurred in SharePoint?