You posted incomplete code as there are a couple of ENDIFs and the LOOP missing.

Try this:
code:
IF Open(1,"c:\sync-c.log") = 0
  $currentline = ReadLine(1)
  WHILE @ERROR = 0
    $lastline=$currentline
    $currentline = ReadLine(1)
    if instr($lastline,'sending') and instr($currentline,'failed send')
      ; failed to send
    endif
  LOOP
  Close (1)
endif
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There are two types of vessels, submarines and targets.