Even if the authenticated user has admin permissions for a Facebook Page, the App still needs to acquire permissions to post on the Page.
Does the issue also occur in the FacebookDemo appliction (included with the TMS VCL Cloud Pack download)?
Can you please make sure the "publish_actions" and "manage_pages" scopes have been added to the TAdvFacebook.Scopes collection (These should have been added by default)? You might want to try adding the "publish_pages" scope as well.
I have not been able to reproduce this issue in the FacebookDemo.
Can you please check if the correct scopes are assigned by selecting the TAdvFacebook control on the form and opening the Scopes editor from the Object Inspector?