nbtscan shows error "Failed to bind: Address already in use"

When using nbtscan with the option "-r", it shows this error:

Failed to bind: Address already in use

The "-r" option is uses local port 137 for scans. Win95 boxes respond to this only. I tried to find which application was using this port using netstat but couldn't find any.

I also stopped samba as some forums mentioned it as the culprit, but that also didn't work.