Take at look at the file in github: https://github.com/nanotechz9l/metasploit-framework/blob/d4f2e72b9cec2b542f94c051965f736cdaaccc5d/modules/exploits/windows/ftp/pcman_stor_msf.rb

I guess there's a problem/difference in the way your editor shows indentation. Try converting Tabs to Spaces and use 2 spaces per indent.