Internal Error #521

  (#96396) Occurred during the macro expansion of an array in a
  REPLACE...WITH...NEXT command.  It was unclear from the example provided
  if the error was caused when a 'M->' preceded the array element, or when
  it did not.  There are indications that the message is sporadic and hard
  to duplicate.

  (#119988) IE #521 occurred in a replace to a memo field. (Note that this  ~
  thread refers to the error as #512, but in the end it was #521 that the
  user was getting)  The error disappeared the next day, no resolution or
  workaround was offered.