I stripped out everything this not essential to see the problem. The file I uploaded works (does not exhibit the problem). To recreate the problem, uncomment the with(plots) line and remove the package name (plots:-). There are four or five places in the procedure. Then you have to reload the worksheet. The proc autoexecutes and you will get the invalid plot structure error message. Clicking the plot button will continue to show this message until you execute the code a second time. At that point everything will work fine. Thanks for looking into this, --Kent

I stripped out everything this not essential to see the problem. The file I uploaded works (does not exhibit the problem). To recreate the problem, uncomment the with(plots) line and remove the package name (plots:-). There are four or five places in the procedure. Then you have to reload the worksheet. The proc autoexecutes and you will get the invalid plot structure error message. Clicking the plot button will continue to show this message until you execute the code a second time. At that point everything will work fine. Thanks for looking into this, --Kent