I created a *.sm file. Everything works well. Then I tried:

1) "Save as..." ".html" file -> error message: "Parameter is not valid"
2) "Save as..." ".xmcd" file -> error message: "Root element is missing"

Anything I should do differently?

I cannot reproduce the issue. Any further info about how to reproduce it? (Program version, OS, steps to create the file, etc...)

Thank you for replying. I'm using SMath 0.99 (build: 7691), Windows 10 on PC. I did some experiment. The file was imported from MathCAD originally and I used it as a template. There appears to be a hidden (white) lines in the file. After I managed to select and delete the lines, "Save as..." for both file types worked.