Error when installing a blogger template, why?

Sometimes you get some ERRORS when installing a blogger template. They can be bx Error Code or double widgets with same ID. The question is WHY?

Blogger Error Codes

In most cases, the installation problems come from EMPTY Blogger widgets. That’s why I always write an installation instruction like below:

1. Go to Layout > Edit HTML
2. Upload XML Template file (DO NOT copy and paste the code directly to template editor box)
3. PLEASE DO NOT PREVIEW YOUR BLOG. Go to Layout > Page Element
4. … The next instruction is about how to fill in empty blogger widgets, especially HTML/Javascript, Text, List, Link List, and Feed widgets…
5. Finish. Preview your blog to see the result.

This is a standard installation instruction for all of XML blogger templates. I know that most of blogger templates don’t have complete installation instruction. But i hope you can get some ideas to avoid ERROR when installing a blogger template.