PCC: no visible global function definition for 'aggregate'
PCC: no visible global function definition for 'update'
ctt2irt: no visible global function definition for 'qnorm'
d4pl: no visible global function definition for 'deriv3'
dm4pl: no visible global function definition for 'deriv3'
gr4pl: no visible global function definition for 'rbinom'
grm4pl: no visible global function definition for 'rbinom'
groupLikelihoodCurves: no visible global function definition for
  'update'
groupLikelihoodCurves: no visible global function definition for 'plot'
irt2ctt: no visible global function definition for 'pnorm'
likelihoodCurve: no visible global function definition for 'gray'
m4plEstimate : priori: no visible global function definition for
  'dunif'
m4plEstimate : priori: no visible global function definition for
  'dnorm'
m4plEstimate: no visible global function definition for 'nlminb'
m4plEstimateMore : priori: no visible global function definition for
  'dunif'
m4plEstimateMore : priori: no visible global function definition for
  'dnorm'
m4plEstimateMore: no visible global function definition for 'nlminb'
m4plEstimateMore: no visible global function definition for 'cov2cor'
m4plMoreSummary: no visible binding for global variable 'median'
m4plMoreSummary: no visible binding for global variable 'sd'
m4plMoreSummary: no visible global function definition for 'cor'
m4plNoMoreSummary: no visible binding for global variable 'sd'
meanModels: no visible global function definition for 'aggregate'
r4pl: no visible global function definition for 'runif'
rm4pl: no visible global function definition for 'runif'
rmultinomial: no visible global function definition for 'rmultinom'
Undefined global functions or variables:
  aggregate cor cov2cor deriv3 dnorm dunif gray median nlminb plot
  pnorm qnorm rbinom rmultinom runif sd update
Consider adding
  importFrom("grDevices", "gray")
  importFrom("graphics", "plot")
  importFrom("stats", "aggregate", "cor", "cov2cor", "deriv3", "dnorm",
             "dunif", "median", "nlminb", "pnorm", "qnorm", "rbinom",
             "rmultinom", "runif", "sd", "update")
to your NAMESPACE file.