Your question is regarding finite element meshing, But unfortunately you posted it in a forum about CNC machining software. There is not a lot of overlap here, so you might not get much of an answer. But you never know who will show up and contribute.
BTW, did you ever notice that Spock-o-file Sheldon's best friend is named Leonard, but nobody ever makes a Nimoy joke? Interesting....
Sorry my reply is not very helpful :-/
I'm glad to help, but I need more information about the issue you're having. When you say you are unable to perform midsurfacing, does that mean you tried and it didn't work? Or does it mean you aren't sure how to perform midsurfacing operations in NX? I would also need to know which version you are using.
If you're unfamiliar with midsurfacing in NX, then I suggest to take a look at the online help documentation which includes a section on midsurfacing. For NX 8.5, you can view this section here: http://support.industrysoftware.automation.siemens
If your problem is more specific, then please reply with more information about the issues you're encountering.