In SP 2010 if you tend to receive an access denied error while crawling a content source which is set with a start address for sps3://hostname ,which is the url for SharePoint sites and its relevant content.
‘Access is denied. Verify that either the Default Content Access Account has access to this repository, or add a crawl rule to crawl this repository. If the repository being crawled is a SharePoint repository, verify that the account you are using has “Full Read” permissions on the SharePoint Web Application being crawled’
The problem could be you might have used an separate least privelged user account as default content access account other than the farm administrator account and that service account may not have permission to crawl the user profiles.
This can happen if your site collection administrator, even if you’re a farm administrator. So what’s the problem? Well in order to manage user contexts, you need to have some manage rights in the User Profile service application as well. You need to specifically get into Central Admin -> .Application Management- > Manage Service Applications. Select the ‘user profile service application’ and click the Administrators button in the ribbon. Add your account that you want to be able to manage user contexts, and grant them at least the Manage Profiles right but I would suggest you to add also ‘Retrieve Data for Search Crawling’ .