Solution
There can be many possible reasons for the NI-RFmx Soft Front Panel not able to launch. You can refer to the below troubleshooting steps to see if these resolve your issue:
1 - If you are trying to launch the NI-RFmx Soft Front Panel from NI-MAX, you could instead try launching it from Start»All Programs»National Instruments»RFmx Soft Front Panel. If you are able to successfully launch it from here then NI-MAX could have some issue and an NI-MAX repair might help to resolve this.
2 - This could be caused by incompatibilities between different RFmx driver components installed on your system. To verify this you could run the Version Compatibility Checker utility located at <NIDir>\RFmx\niRFmxCompatibility_Checker.exe & see whether any incompatibilities are reported.
3 - If you are logging into a Windows PXI(e) controller remotely via VNC or Windows Remote Desktop, please check whether there is a display monitor connected to the controller & whether it is switched ON. If a display monitor is connected and is switched OFF, then the RFmx Soft Front Panel might be automatically loading onto it. Powering ON the display monitor or disconnecting it might solve the issue.
4 - If none of the above steps solves the issue then the NI-RFmx drivers might have gone corrupted. Try repairing NI-RFmx components using NI Package Manager.