"the enablesessionstate attribute on the page directive is not allowed " suddenly on sharepoint application page -

i have moss site working fine, database server migrated , working application page showing error "the enablesessionstate attribute on page directive not allowed on page".

here following things tried:

1. check ssp session configuration
2. validated webconfig for: session module , , page enable session state tags.
3. even application page have enablesessionstate page directive set true.
4. asp.net session state service running

significant observations: 1. broken site uat site , same code working in production , database migrated both. 2.both environment have same code , same configuration. 3. when using other master page issue resolved setting required masterpage again causing issue. 4.prod masterpage copied on environment giving error.

any thought on highly appreciated.