I had no problem running this VI. Since I didn't have the VI you are using with Append Front Panel Image to Report (your VI is called X crossing3.vi), I used my own VI with a chart on its panel...when I generated the report, it came out fine. Do you have the X crossing3.vi open when you run the HTML Report Generation.vi? Since you are using the VI name as a string (as opposed to a path), the VI must be open when you run the report generation VI, otherwise no front panel will be appended. If your X crossing3.vi is not open for whatever reason, you can wire a path to Append Front Panel Image to Report instead of a string.
I hope this makes sense. If you're still having trouble, please attach any additional VIs to your response that I would need to reproduce the problem. Also, give me the exact steps to what you're doing, and the resulting problem you're seeing.
Good luck,
-D