I cannot make ANY change with SPD to an aspx page I created with SPD and get it
to display either in SPD or in the UI. I can't even insert a blank into the
<style ..... /style> anywhere, or change 1 digit of a color specification.
Further, after a simple change, & save, and failure, then trying to restore to
prior version also will not display. (MOSS enterprise site)

In SPD in its web-zone I get message:
"this web part does not have a valid XSLT style sheet...the file does not exist
or you do not have permission to access.

Roughly what I've done is:
1. create a DFWP view using SPD
2. modified some of the <style...../style> items for display formatting
3. changed the defaults so that "items rendered=all" and "cache=no"
4. made sure this worked in SPD and the UI
5. now the big change, in UI xsl edit window replaced everything between
<xsl...../xsl> with an xsl include of my own XSLT that has been tested on my
client PC
6. these xsl lines/file are stored in the style library of the root site of site
collection

This runs fine, and I can even change the xsl stored in library fine for
different paramters of the display.

BUT, I cannot go back and with SPD change anything on the aspx page at all.

Is this really a permissions problem, or some quirk with SPD? How to fix so that
I can control formatting, colors, etc. with css styles in SPD, and control
content with my custom XSLT code?