ISIS NAC Image header issue

I am trying to convert the LROC NAC image to the cube. Whenever I try to convert it using lrocnac2isis, it shows me the following error-
“I/O error- The PDS header is missing important keywords.”

Hi can you tell us what files you are using, where you got them from, and the exact command you are running?

Steps I have followed:
I have downloaded all the LRO data.
Then search for the specific area data using LROC quick map and the URL to download the (CDR and EDR) NAC data (‘wget’ command). I have downloaded the M169698677RE.IMG.
All the datasets are in a separate folder in ISISDATA>LRO folder.
After navigating to the LRO folder, I used lronac2isis command to convert it in the cub and got this error.

Update: I figured it out. I have named the isisdata as $isisdata. So it was showing an error in the path. I have rectified it. Thank you for the help.