Virtualbox Port Forwarding Problems

I've recently started using VirtualBox and find it really good. However, I was setting up port forwarding with NAT according to the documentation and must have made a mistake since I got the following error while restarting the virtual machine

I tried to remove the newly added settings using but I guess I had a typo somewhere in my initial attempt to use setextradata, and I couldn't figure out what the typo was (I had closed the command prompt window and there was no history available). I couldn't find anything online using google so I simple deleted the virtual machine and added it again using the same vdi...worked like a charm. Hope this helps someone out there.