I encountered this error while configuring DBAMP on one of the Production Server, had to work with Salesforce Support team to understand and fix the problem. Useful notes for reference:
• What is the Error while importing data or testing a connection: Error: Invalid Serial Number. Please contact forceAmp.com for a valid key.
• Sandbox works as expected, error is only in Prod: Yes, I don’t see any problem with Sandbox/Dev, the problem occurs only in Production. I believe License validation occurs only in Production environment.
• How to Test: c:\Program Files\DBAmp\DBAmp.exe -> Configuration -> Test Connection -> Enter User Name, Password -> OK
o Check if DBAMP is upgraded to at least V2.16.8 version or not: c:\Program Files\DBAmp\DBAmp.exe -> Help -> About DBAMP
o If running with old version, upgrade to latest version.
• Serial Number:
o Check if the Serial Number is valid or not, update. c:\Program Files\DBAmp\DBAmp.exe -> Configuration -> Options -> Serial Number 1/ Serial Number 2/ …
o If you are pulling from different databases, you need to have different Serial Numbers. You have option to include 4 Serial Numbers in the configuration
o You may have to work with your Org license manager to get the Serial Number