>> Database 18.5.1596 Code 18.4.1384."
This means that your databases are showing a version of GP at 18.5.1596 but your code, specifically the Dynamics.dic file, is still showing 18.4.1384.
Along with what has been stated here, you can try re-applying the 18.5.1596 patch onto this machine's GP install and see if it then begins showing as 18.5.1596 also.
Otherwise, you can try renaming the Dynamics.dic file, then in Control Panel, run Repair against GP which should re-create that file, hopefully at the 18.5.1596 version.
If neither works, you'll probably need to uninstall and reinstall GP at the 18.5.1596 version on this machine.
Copying GP directory files sometimes work, but in most cases, it doesn't align with what is written in the Windows Registry of that machine, so has the same issues.
Thanks