I'm happy that this problem was solved for folks in this thread from five years ago. But the solutions described here did not solve the very similar problem I was having setting up the Nektar Impact LX25 control surface with Cakewalk SONAR X3 running under Windows 10. In my case, the control surface was showing up in parentheses and the MIDI ports were not staying assigned as described by Rynan Munnis in this thread. There is only one installer for the Impact LX25 that handles both 32-bit and 64-bit installations, so that was not the problem. What was particularly vexing was that I could set up the control surface with my laptop but not my desktop, even though they were running the same software. After a couple of weeks of intensive back-and-forth with Nektar tech support, we discovered the problem, and I thought I should share the solution in case someone else encounters it.
One requirement for the Nektar Impact to work with Cakewalk SONAR is an appropriate version of Microsoft Visual Studio redistributable. What happened in my case was that the Nektar installation program included a version of VS that used to work, but, unknown to Nektar, Cakewalk SONAR 3 upped their requirement to a later version. Now, VS is often installed with all sorts of other software, and because I use my laptop for many things, it had the required version of VS from the installation of some other program. But I had been purposely keeping programs off of my desktop computer except for music recording and production, so it did not have the required version of VS. The problem was immediately solved by installing the latest version of VS. Naturally, Nektar said that they would revise their installer to include the needed version of VS. But if you have the symptoms described here, this might be the issue.