You may be coming across this error when trying to browse to a SharePoint site resource such as an image, list or library. In my case it was caused by adding a new link to a site navigation structure and browsing for a resource to populate the URL field. The issue is related to the Office SharePoint Server Publishing feature and the entities created or “connected” on activation. When the publishing feature is activated in a site, among other changes, a document library called Documents is created. This document library URL then becomes the starting point for the AssetPortalBrowser. The URL: sitename/Documents/forms/allitems.aspx must point to a document library in the publishing site although the library can have a different name.
SharePoint thinks he has avoided any issue here by removing the option to delete this library BUT there is a chink in the armor. If a document library called Documents is created while publishing is not activated in the site, when it is eventually activated, SharePoint does not bother creating the Documents library because it already exists. The problem is that now, because the user created the library, they have the option to delete it.