Just a quick one this time. When you create a custom masterpage for your SharePoint environment and upload that into the masterpage gallery, you will have to publish it before readers will be able to access the portal. Otherwise they will get a “File not found” message when trying to access a page. The masterpage gallery itself is a SharePoint document library with versioning and approvals enabled. When you first upload a masterpage, the status is “Draft” and therefore only visible for administrators.

Something that is very obvious afterwards, but took me (and other people) some time to realize.