PERT Error in Project

[Azza117]

Hi I am trying to use the PERT analysis within Project, but when I try to use either the PERT Entry Sheet or the optimisitic / expected or pessimistic Gantt I get the following error:

"An error occured in the COM Add-In named: PERT Analysis Error #:1101"

Does anyone know how to rectify this? I have checked to see that the Add-In is loaded, which it is.

Thanks!