If it just your local PC and want to use it locally, remove the full host name ("MMAGAN-NL.nl.oracle.com") from the listener.ora file and use just localhost, then stop and start the service.
It is probably a firewall thing, we had a similar issue on local PCs using a full network name when we were not connected to the VPN...
Thanks, that worked. Additional info for future reference:
- Disabling the firewall did not resolve the issue
- Issue only occurred when VPN active, so likely related to this.