The entire site is blank/white right now. I will return to my original point, though.
WordPress has a number of template file names that it looks for to display particular pages. These are the reserved file names I mentioned.
archive.php is one of them.
When constructing a theme you can add your own templates by creating a file and adding something like (fron the Codex)...
Template Name: Snarfer
... to the top of the file.
Reserved file name files do not show up in the choose a template box on the page edit screen. 'Template Name' files do show up there.
You should either name a file
archive.php, leave out the 'Template Name:' part, and let WordPress use it as that file is intended, or name it something else--
kinda-archive.php--, add the 'Template Name:' part, and select the template when you add a page. You should not do both. Doing both can cause some maddeningly frustrating weirdness. I've done it. I couldn't figure out why it sometimes worked and sometimes didn't until I realized that I'd used a reserved file name for my custom template.
I don't know if that is your problem but is is something to consider well. The fact that it works sometimes isn't really proof that this isn't the problem. I experienced the same thing.