If you have deployed a SharePoint FAST Search Server with the RTM version of SharePoint 2010 you will notice that after the creation of the FAST Content Search Service Application the account that is running the SharePoint Server Search 14 (OSearch14) service is the Server Farm Account (or known as the Database Access Account).
This was a bit unexpected (to me anyways) and if you apply the October 2010 Cumulative Update to your SharePoint Farm and run the SharePoint Configuration Wizard this account will be changed to the account you had originally specified as the Search Service Account (dev\_fs_cssa) at which point if you already performed the steps necessary in Configure SSL Enabled Communication you will need to rerun the command otherwise your event log will start to fill up with SChannel errors due to the account running the OSearch14 service not having access to the certificate.
.\SecureFASTSearchConnector.ps1 -certPath ".\certificatename.pfx" -ssaName "name of your content SSA" -username "domain\username"
So you may have originally run this:
.\SecureFASTSearchConnector.ps1 -certPath ".\certificatename.pfx" -ssaName "FAST SSA" -username "dev\_ap_farm"
You must rerun it with the updated account:
.\SecureFASTSearchConnector.ps1 -certPath ".\certificatename.pfx" -ssaName "FAST SSA" -username "dev\_fs_cssa"