How are these links created?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

• 
  Athanasios Giannias: Hi everyone
  
  Trying to overcome one obstacle after the other. Will be done with the help of this community.
  
  Please have a look at the snapshots from webmaster tools, under crawl -> crawls errors. I have no idea how these links are created. I have 301 redirected many, but over time many are created again.
  Have installed a sitemap generate module.
  
  Is it possible i have wrongly configured the site map module? Maybe the problem lies within my back-office?
  
  Any help is more than appreciated.
  
  Thank you all
• 
  SEMXE: hey +Athanasios Giannias, it seems like there are a lot of dynamic urls getting generated at your end. The simplest solution would be block these from robots.txt file.. using this instruction - ;Disallow: /% (assuming you are not using % in any of your URLs intentionally)
• 
  Marty Eigner: You can tell which and how you want your parameters crawled under the same Crawl tab in 'URL Parameters'
• 
  Athanasios Giannias: thank you +SEMXE ;Its not only the %. Look at these links:
  
  en/content/-  ;  ;
  el/off-road/735-  ;  ;
  el/blog/-10p1  ; ;
  3632/
  el/index.php?controller=  ;  ;  ;
  el/π
  el/new-products
  el/manufacturers
  
  I have many links like these that point no where. ;
• 
  Athanasios Giannias: thank you +Marty Eigner ;Is it normal for a site (ecommerce if it matters)  ;to generate these types of URL's?
• 
  Marty Eigner: Many e commerce sites have these urls and generally you don't want them as they are duplicate content. Also you can get hit by #Panda if you have too many thin pages like these indexed. 
• 
  Athanasios Giannias: Not intentionally done. Auto generated they are. They point to non existing pages.
  
  Best way to solve this problem is via the URL parameter or block these from robots.txt file?  ;
• 
  Marty Eigner: Just tell Google not to crawl them via URL Parameter
• 
  Athanasios Giannias: never used this tool. It scares me :) ;
  
  Last thing: there is a blog on my site  ;http://...../el/blog
  
  How do I tell google via the URL parameter not to crawl ->  ; el/blog/-10p1  ; }} which points no where
  
  Thank you +Marty Eigner ;for you time
• 
  Marty Eigner: https://support.google.com/webmasters/answer/6080550?hl=en
• 
  promoz seo: Create custom error pages with .htaccess and also use rel=canonical tag on each page, this is very very important. As everyone said URL parameter tool has to be used.
  CMS software always tends to create duplicate URLs like these which cause duplicate content issues which is surely not good for SEO and user experience.
• 
  Athanasios Giannias: Thank you +promoz seo ;I aapologize for the question. ;
  
  The below links must have: "Doesn't affect page content". Correct?
  
  modules/productquestion/productquestion-form.php?id_product=1002
  modules/productquestion/productquestion-form.php?id_product=1007
  
  el/index.php?controller=attachment?id_attachment=2
  el/index.php?controller=category?id_category=115&p=2
• 
  Elisabeth Bobeck: I agree, I added a disallow / statement to my robots.txt file for all the events I host at one of my sites. I enjoy webmaster tools, but I do not like all the errors it sends me, but thanks to this group +Dumb SEO Questions ;
• 
  Tony McCreath: Checking one of the "linked from" URLs and I see you have a 302 redirect in place that leads to a 301 that creates these error URLs.
  
  It looks like the initial redirect is meant to switch from www to non www and the second one is meant to switch to a new product URL structure. Both are messed up:
  
  First. It should be a 301 redirect as you are trying to ensure all indexing is on one site. ;
  
  Second. It is adding the parameter to the destination URL as well as passing on parameters. This means it is adding two sets of querystring to the destination URL. ;
  
  Third. In this case the product.php is again redirects (a 301 this time) to the final URL. This is creating another querystring which the previous querystring is being bolted on the end. So you now have 3 querystrings added end to end with the last one being encoded which is why you see the %3f (The encoding for the start of a querystring (?)).
  
  Conclusion: your redirects are a mess. ;
  
  This will show you the path Google followed from that linked from URL:
  
  http://bit.ly/12vOFNx
  
  You need to fix the redirects in all those steps so Googlebot ends up on the correct product page. Then to get rid of the errors you could devise more complex 301 redirects to redirect the broken links you have created with these mistakes!