Error in .local(x, values, ...) :
  values must be numeric, integer or logical.

inR <- 'D://test/TS_combined_clipped.tif'
outR <- 'D://test/R_test3.tif'

rasterB <- brick(inR)
fun1 <-function(x){
  years = c(1972,1973,1974,1975,1984,1984)
  na_idx = which(is.na(x))
  years = years[-na_idx]
  x <- na.omit(x)
  idx = detectChangePoint(x, cpmType='Student', ARL0=500)$changePoint
  return(years[idx]) # this raises error
  # print(years[idx]) # This does *not* raises any error
}

r <- calc(rasterB, fun=fun1, filename=outR, overwrite=TRUE)