Today I migrated a SharePoint 2010 publishing site content database to our Azure staging farm. All went smooth after using sp_changedbowner on the restored database before adding the content database to the web-application using Central Admin. However, when I tried to browse the publishing site, I got the "an unexpected error has occurred" message. Browsing /_layouts/settings.aspx worked fine and so did browsing "all site content" and the /pages/ list settings.
Using the correlation ID in combination with the ULS viewer lead me to this infamous portal sitemap provider exception:
DelegateControl: Exception thrown while adding control 'ASP._controltemplates_publishingconsole_ascx': Object reference not set to an instance of an object.
PortalSiteMapProvider was unable to fetch current node, request URL: /Pages/Forsiden.aspx, message: Object reference not set to an instance of an object., stack trace:
at Microsoft.SharePoint.SPField.GetTypeOrBaseTypeIfTypeIsInvalid(SPFieldCollection fields, String strType)
Googling a "PortalSiteMapProvider was unable to fetch current node" exception is no fun. You will typically get it in relation to top navigation and related site map providers. I've chased the cause of that error before, and sometimes had to resort to iisreset each night due to the publishing cache going corrupt over time.
This time, luckily, the exception details indicated a problem with the /pages/ list item definition, which led me to How to fix "System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.SharePoint.SPField.GetTypeOrBaseTypeIfTypeIsInvalid" that helped me solve my problem. By looking closer at the list settings for the pages list, I could see that a list column was flagged as invalid (look for the text "Delete this invalid field").
Trying to browse to Site Settings > Site Columns didn't work, but it gave me the enough information to find out what caused the issue and helped me solve it:
Field type AdvancedCalculated is not installed properly. Go to the list settings page to delete this field.
Deploying the missing feature to the staging farm solved the problem. Now it only remains to fix all those absolute URLs entered by the content authors.