If your VFD is throwing a NTC Open fault code there are a number of things that might be the issue, 

In the case of IG5A, check to see if NTC resistance of the PIM is normal. Also make sure to check the IS7 to see if the thermistor resistance is normal. If the answer is no to both then replace the PIM or NTC thermistor. 

Next, check to make sure the NTC is wired correctly. If it isn't then change the wiring to the correct specifications. 

If the wiring isn't faulty check to make sure the voltage of the SMPS is delivered normally from NTC to control the PCB. If it isn't then change the SMPS. If it the voltage is correct then the control PCB is most likely the problem and needs to be changed.