After a model is translated and run in Visual MODFLOW Classic, when viewing the output from the output section, the user selects Graph > Calibration > Heads
The cause of this error message is the options for PEST have not been defined.
To use the Graph > Calibration option in the output, PEST needs to be run with MODFLOW. To run PEST with MODFLOW head observation wells should be defined in the model. Once this is defined, in the Run section of the model use the Optimization > Parameter Optimization option:
Refer to the page 432 “Parameter Optimization: PEST and Predictive Analysis”: https://waterloohydrogeologic.com/help/vmod/VMOD-2011.1_Manual.pdf
After this you will be able to run MODLFOW and PEST together and then switch to the graph > calibration in the output section.
Hope this helps!