Error from getSRAfile function in SRAdb package

Question

I am trying to download RNASeq data from NCBI SRA repository using SRAdb package. I consistently get the following error:

getSRAfile( in_acc = c("SRR2033366", "SRR2033446"), 
  sra_con = sra_con,
  destDir = getwd(), 
  fileType = 'sra', 
  srcType = 'ftp', 
  makeDirectory = FALSE,
  method = 'curl',
  ascpCMD = NULL)

Error in if (is.na(sra_acc$run[i])) { : argument is of length zero