To debug NSE scripts, use --script-trace. This enables a stack trace of the executed script to help you debug the script execution. Remember that sometimes you may need to increase the debugging level with the -d[1-9] flag to get to the bottom of the problem:
$ nmap -sC --script-trace <target>$ nmap --script http-headers --script-trace scanme.nmap.org NSOCK INFO [18.7370s] nsock_trace_handler_callback(): Callback: CONNECT SUCCESS for EID 8 [45.33.32.156:80] NSE: TCP 192.168.0.5:47478 > 45.33.32.156:80 | CONNECT NSE: TCP 192.168.0.5:47478 > 45.33.32.156:80 | 00000000: 48 45 41 44 20 2f 20 48 54 54 50 2f 31 2e 31 0d HEAD / HTTP/1.1 00000010: 0a 43 6f 6e 6e 65 63 74 69 6f 6e 3a 20 63 6c 6f Connection: clo 00000020: ...
