Hmm, problem:
Error: Invalid subsystem name.
In sexpression: ( when 
   ( has-arrived-delay 6 "Cypher" ) 
   ( fire-beam 
      "Cypher" 
      "turret12" 
      "Ithaca" 
   )
   ( fire-beam 
      "Cypher" 
      "turret20" 
      "Ithaca" 
   )
)
(Error appears to be: turret12)
File:E:\Languages\Visual Studio Projects\Visual C++\fs2_open\code\Mission\MissionParse.cpp
Line: 4539
Call stack:
------------------------------------------------------------------
------------------------------------------------------------------

Encountered it just after finishing the mission where the derelict first appears, if that's any help.