Sometimes I copy a valid model such as "Model A," then I either use the automatic label "Copy of Model A," or I change the name, "Model B." In either case the new model (the old model with the new name) won't run and I get the message "There must be a valid pathmodel for calculation." Also now the original Model A won't run either, although Model A ran successfully before I made the copy. What can I do. i suspect the program doesn't recognize the model name after the copy has been made. Thanks in advance.