Error Message: Invalid Company Reference Key XXXX Returned when Submitting an Online Case Form

The reason on why the error shows when customer submits the Online Case Form is because the Anonymous Place Holder under Setup > Support > Case Profiles is Inactive.

This also would happen when the checkbox Create New Lead on No Match is not checked under: Setup > Support > Support Preferences > External tab.

To resolve the problem, select an existing (active) Anonymous Customer Placeholder or check the Create New Lead on No Match checkbox so NetSuite can create a new Lead record when information on a case submitted through the external case form does not match any existing records.
  

1. As Administrator navigate to Setup > Support > Support Preferences.
     2. Click the External tab. 
     3. Check Create New Lead on No Match checkbox. 
     4. Click Save.

Or

     1. As Administrator navigate to Setup > Support > Case Profiles.     
     2. Edit the Case Profile defined on the Online Case Form. 
     3. Click the General tab.
     4. Change the name set in Anonymous Customer Placeholder field or create a new one.
     5. Click Save.