The first you think when you see this is that you don’t have access in the ACL or that the document has reader or author name fields that is blocking you from updating the document. But there is another option on the database that can give this problem.
On the advanced tab “Maximum Internet name and password” must be set to the level you want a user maximum to have. This will block any other user acess set in the ACL so if you set Reader here all XPage users will be readers even if you assign Editor, Designer, Manager in the ACL.
Took me awhile to remember this option when I got this error, then it’s time to write a post about it.
Do you have similar hard to find errors that you have solved for XPages, make a comment with a link to your blog or write directly in the comment.