Package check result: ERROR

Check: examples, Result: ERROR
  Running examples in ‘IrregLong-Ex.R’ failed
  The error most likely occurred in:
  
  > base::assign(".ptime", proc.time(), pos = "CheckExEnv")
  > ### Name: abacus.plot
  > ### Title: Create an abacus plot Creates an abacus plot, depicting visits
  > ###   per subject over time
  > ### Aliases: abacus.plot
  > 
  > ### ** Examples
  > 
  > library(nlme)
  Error in library(nlme) : there is no package called ‘nlme’
  Execution halted