In the numerous FAST configurations the error above is the most common and one that I wanted to share my experiences with. There is a number of issues that might be causing this error and renders FAST Search unable to crawl. This issue can be from the initial configuration of FAST, but can also be introduced later on if you modify the deployment.XML and reconfigure FAST.
Here is the list of the most common ways of resolution and is in the order of :
1. Secure the connector by running
.\SecureFASTSearchConnector.ps1 -certPath "path of the certificate\certificatename.pfx" -ssaName "name of your content SSA" -username "domain\username"
replacing the necessary parameters with the values for your environment. Here are the detailed instructions http://technet.microsoft.com/en-us/library/ff381261.aspx
2. Check if the domain and user name is reflecting the details of the user running the SharePoint Server Search 14 (OSearch14) service. The user account running Server Search 14 service should be the same as the user name used to secure the connector.
3. Make sure that the content distributor URL is the same as in the Install_Info file located within your FASTSearch folder or the same as in the fastsearch\etc\contentdistributor.cfg file – sometime that might be the issue is the value in the install_info file is not the same as the cfg file, use the URL from the CFG file.
Hope it helps.