Sharepoint Crawler is denied access to sites - sharepoint

Question

We create all our site collections programatically with a custom site def/template. Everything works as expected, except for the crawler. It's apparently denied access to the sites. The crawl logs says:
http://server.localnetwork.lan/somesites/siteName
The object was not found. (The item
was deleted because it was either not
found or the crawler was denied access
to it.)
And in the log files I'm getting this:
08/11/2009 14:20:34.01 OWSTIMER.EXE
(0x0674)
0x1560 Search Server Common
MS Search Administration
7hmh High exception in
SearchUpgradeProvisioner Keyword
Config
System.InvalidOperationException:
jobServerSearchServiceInstance is null
at
Microsoft.Office.Server.Search.Administration.SearchUpgradeProvisioner..ctor(SearchServiceInstance
searchServiceInstance) at
Microsoft.Office.Server.Search.Administration.OSSPrimaryGathererProject.ProvisionContentSources()
If I create a site collection manually the crawler is able to access it. The same users/accounts have the same access on both sites, so that shouldn't be the issue.
The code we use to actually create the site collection looks a little like this:
SPWebApplication app = SPWebApplication.Lookup(new Uri("WebApplicationUrl"));
app.FormDigestSettings.Enabled = false;
app.Sites.Add("url", "title", "description", "language code", "SiteTemplateName", "Owner.Username", "Owner.Fullname", "Owner.Email");
app.FormDigestSettings.Enabled = true;
The code has been slightly altered to protect the innocent... ;)
Any idea what we're doing wrong?
(Please note, I'm not sure if this is a programming error or a config/setup error, so I'm cross-posting with Serverfault)

Answer 1

If you receive this error whilst the crawler account (the default content access account) has read permission to all your sites then you most likely need to disable the loopback check.
http://support.microsoft.com/kb/896861
http://koenvosters.wordpress.com/2009/06/15/access-denied-when-using-hostname-search-and-site-on-moss-2007/