The best replacement for error is mistake.

The best alternatives to error are rated as following:
★★★★★  mistake
★★★  standard deviation
★★  err
★★  uncertainty
★★  exception
★  systematic error
★  random error
★  omission
★  residual
★  bias
★  no keyboard present
★  relative error
★  err on the side of caution
★  media is write protected
★  defect
★  difference
★  type ii error
★  type 2 error
★  hit
★  misconfiguration
★  failure
★  exception java
  fraud
  percent difference
  server not found
  percentage error
  violation
  deviation
  fault
  variance
  fatal
  standard error
  warning
  change in estimate
  computer error
  coefficient of variation
  accuracy
  exception in java
  absolute error
  bug
  sampling bias
  exception c++
  % difference
  blue screen
  standard error of the mean

Your alternative for error is not listed? Suggest!
Speaking about error, one probably shouldn't forget about sample size.

Other search terms related to error and their ratings are:
★★★★★ sample size
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Google Trends

Scale is based on the average worldwide traffic of error in all years. Click on graph for more.
error
mistake
standard deviation