N30274 is the name of the net connecting two parts. If you go to your top level in the design explorer and do a search with that name you will find it. Orcad auto generates net names for every wire connection you make.
Like Andy says it's trying to warn you that you have an input with no output, but it's probably not an issue. If you edit the part in the library and right click on the pin I think you can see properties. One will have a pull down for input, output, passive, etc. if you set it to passive for both parts connected to that bet the warning will go away.
Personally I never use this feature and just set things to passive all the time, but it could be useful say to protect yourself from hooking up a serial port wrong. It only makes sense if when you build all your library parts that you set the correct attribute for each pin. Otherwise you'll always find warnings like this.