It means you forgot to connect a wire someplace in your circuit, check out picture i attached, you should attach urs too if still giving you problems.
To help find the location of those troublesome nodes, go to 'Edit - Find' or press 'Cntrl+F' and and type in the name of the wire giving you the problem, in your case type 'N06363' and select the Nets bubble under the scope. It'll highlight that node in your schematic for you. And sometimes i get that error when i forget to connect a '0' ground symbol on my circuit, just returning everything to a source is not enough for pspice, it likes to see that ground symbol connected someplace in there.
Well, it looks like some of the parts you are using dont have the capability to simulate. Your NAND gates for example, i show a picture of what to look for in a part that is able to simulate. i didnt check all your other parts, some of them might have the same problem.
Some years ago I evaluated ORCAD. And orcad at that time did have the PSPICE A/D simulator. That will say you can simulate your design. But as Masa6614 says, you have to use another library for the digital functions. This link may help http://users.ntua.gr/manias/PSPICE-4.pdf
i have a problem to simulate in Pspice where when i simulate it give me error like this:
ERROR(ORPSIM-15108): Subcircuit 74LS157 used by X_U33 is undefined
what should i do????
please help...