When you create a site template in Sharepoint 2010 where the template is taken from a site that has an alternate CSS url set, you find on the newly created site that when you try & access ‘Site Settings’ or ‘View all site content’ you get the ‘An unexpected error occured’.
In your logs you get something like:
System.Web.HttpException: Error executing child request for /sites/SiteName/Style Library/site-style.css
This appears to be a bug, you can fix the site by running the following Powershell script:
$w = Get-SPWeb http://YourServer/YourWeb; $w.AlternateHeader = $null; $w.Update()