The Access Manager works perfectly for all other pages.
The insert and update pages is where the errors occur.
When opening each of the above 2 pages to add the Restrict Access Server behaviour, I get the same first error as before. Eventually the page does display. When I add the Restrict Access Server behaviour, the same error occurs again, but after a couple of seconds the restrict access code is placed in the head region. When testing the page, access to the page is restricted and redirects to my login failed page.
To test, I completely shut down Dreamweaver, re-opened and opened each of the referred to pages again. The first error appears again.
Fortunately, the pages are working fine.
Thank you Jason for the advice.