I've been searching through the forums and the codex trying to sort this issue out, but I keep having problems and so far haven't found a thread that adequately addressed my issue.
My approach is relatively simple. I find a theme I like but want to modify slightly.
1) I download it
2) I copy the theme folder and rename it
3) I open the stylesheet in the new folder change the details at the top of the page ala: http://codex.wordpress.org/Theme_Development#Theme_Style_Sheet
3) I upload the folder to my wp-content/themes folder on my server.
4) I go to the theme manager page in the WP dashboard and invariably get some version of: "The following themes are installed but incomplete. Themes must have a stylesheet and a template."
Somehow in the past, various versions of the details at the top of my style.css page actually worked, I was able to upload the theme, change the style sheet and preview it sucessfully. Overnight something changed and I can't preview my old theme, nor the new theme I'm trying to work on.
The error message that implies that there is no stylesheet or template in the folder is confusing. The theme that I'm modifying is one that is fully functional and presumably has all the necessary parts. Presumably also the theme should be able to stand alone rather than be based on a template in another folder... so why am I having this problem.
Rather than try to create a new theme from scratch, it makes sense to me to try to learn about it by tinkering with different parts of a theme to see how my changes work.
Three major questions I need answered:
1) Other than changing the details at the top of the style-sheet, is there some other thing that I'm neglecting to change to make the theme act as a new separate theme?
2) Can someone point me in the direction of a clear directive as to how best to write the details in the stylesheet so as not to break the theme. (I've already read the codex page postd above, which is kinda vague on details)
3) Am I actually missing the templates if they are templates that work for a pre-existing theme?
Thanks for your help. I'm new to this... so detailed responses would really be appreciated. I am spending a lot of time in the codex trying to sort this out.