The FAST Search certificate in the Customer Immersion Experience (CIE) v3.5 expires on June 15th 2012.
Here's how you can renew the certificate.

 

In the FAST PowerShell Command Prompt

Stop all the FAST Search Services

net stop FASTSearchMonitoring
net stop FASTSearchService
cd C:\FASTSearch\installer\scripts
.\ReplaceDefaultCertificate.ps1 -generateNewCertificate $true
 

Restart the FAST Search Services

net start FASTSearchService
net start FASTSearchMonitoring
 
 

In the SharePoint PowerShell Command Prompt  
cd C:\FASTSearch\installer\scripts   
.\SecureFASTSearchConnector.ps1 –certPath "..\..\data\data_security\cert\FASTSearchCert.pfx" –ssaName "FAST Search Content SSA" –username "contoso\administrator"

Perform the IIS reset
 iisreset