[erlang-questions] How find the root cause of "Bad value on output port 'efile'"

[shiker2003]

Hi everyone,
   I developed a tool(using socket to send data) to simulator lots of simulation terminal,which send its fake data to server. I use this tool to perform performance test. log4erl is used to print log message to file. "Bad value on output port 'efile'" comes out ,I have no idea how to find the root cause for it. 
   I tried to get some help from search engine,but it helps little. While I find some posts about "Bad value on output port 'tcp_inet' ", which is caused by bad argument in gen_tcp:send . 
   I guess efile has some thing to do with file operation ,like writing data to file etc. but I didn't operate with file directly. The only one module works with file is log4erl, for this module writes some log file. Another point you need pay attention to is that ,the error is random. 
   Any suggestion or help is appreciate.
  
 Best regards,
 Eric Sun.
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