Poor URL structure is a frequent SEO issue, one that can impair rankings, keep pages out of the search engine indexes, and suck ranking authority from your other pages or even the entire websites.
Some content management systems bake poor URL structures right into their websites. Lax rules can be a culprit, for example, not encoding spaces or special characters.
Meanwhile, some CMS platforms devise URLs using illegal characters that should not appear in addresses. Others generate multiple URLs for pages, creating duplicate content.