Thanks for your reply Nancy,
Point taken. The original structure code for the site was written many years ago and clearly needs to be cleaned up and made more consistent. But would this cause design view in Dreamweaver to suddenly stop working since it worked for years in the past? Or am I missing some setting in Dreamweaver?
Is that page you posted above from your site's main homepage? (the one at www.yoursite.com?)
If so, the link showing...
../SpryAssets/SpryCollapsiblePanel.js
...would be telling DW to go up one directory level from the site root, which DW can't do. All files must be within the directory set in your Defined Site.
If you're trying to save yourself some duplication by linking to a common file outside of the Site Defintion, DW won't know what to do with it.