[Limdep Nlogit List] Variance of parameters: Parametric Duration Model

[Zainab Jamal]

Hi
  In the parametric duration models (weibull), 
  lambda=exp(-beta*X) and I get estimates of beta and also its varcov matrix when I run 'SURVIVAL'.
  How do I get the varcov matrix or variance of lambda from the estimates of beta?
  Any literature reference would be helpful.
  Cheers
  Zainab