It is possible that the client did receive their access code, but it may have been filtered into their junk/spam folders or through their internal quarantine.
If the the access code reads "No data", it could mean that an access code was not requested.
With business returns, the client must request the code.
You will then be able to see the code that was requested in SafeSend Returns:
If the Access Code shows "Expired", you are given the option to "Generate Access Code"