An unexpected error has occurred when entering site collection administrators page (_admin/owners.aspx)

The problem occurs when the default / root site is loaded with an error and prevent of changing the primary and secondary site collection administrators.

There are three workarounds to solve this problem: 

1. Obtain the siteID from SQL and then append it manually to our request for owners.aspx

for example: http://moss:3653/_admin/owners.aspx?siteID=SiteGUID

NOTE: Never update any SharePoint database directly.
Always use the SharePoint API (Object Model) for any updates.

To obtain the siteID all you need to do is to run this query in SQL studio management

USE [Content DB]
SELECT SiteId AS SiteGuid, Id AS WebGuid, FullUrl AS Url, Title, Author, TimeCreated
FROM dbo.Webs
WHERE (ParentWebId IS NULL)

stsadm -o siteowner -url http://moss -ownerlogin DEMO\Admin1 -secondarylogin DEMO\Admin2

3. Through Site Settings - Navigate to this URL: http://moss/_layouts/mngsiteadmin.aspx and add or

remove site collection administrators.

Enjoy!