Why cannot edit views because "The requested page could not be found." I am having a sudden error on a drupal site I inherited in that I cannot edit views anymore, any of them. One moment I am able to open a view for editing by clicking the edit link on the all views list and the next moment the edit link results in 


  The requested page could not be found.


for all views. 

The only change I made was to change the display on a field from do not display to display for a specific view. I then updated the view and saved it. At first the save did not work, but then I clicked again and it saved. The field I wanted displayed but now I cannot reach the edit screen for any of the views. 

The log only references the 404 error, but nothing as to why, my apache log is equally unhelpful in determining why this has become the case suddenly.

The rest of the site, so far as I can tell, is running as usual and I can still list the views and see the actual views when going to their paths.

Update (problem solved but question remains): I drush cc all (cleared the cache) and the view edit pages are reachable again. 
Though for future reference, what might be the reason that this happened? I feel like this isn't the first time I've found Drupal acting unpredictable and that clear the cache sets it straight.
The update to your original question suggests that the problem wasn't with Views itself.

When you do a drush cc all, it essentially calls drupal_flush_all_caches(), which


clears the JS cached files
clears the CSS cached files
rebuild2 the list of themes
rebuilds the theme registry
rebuilds the menus
rebuilds the list of content types
deletes all temporary items from the cache bins, and all items that had TTLs set which have expired


What I suspect, is that something happened to the menu tables and the cached entries were not fully rebuilt (I have seen this before).  Typically, it happens when you do a cache clear from the Performance page, and the process barfs, normally from running out of memory or timeouts because of load (I have seen the later on some servers).

When you did this from the command line, the menu tables got fully rebuilt that time, and your pages are available.

You should keep an eye on the amount of memory your site is using for page requests from a stale cache, and compare with the PHP memory_limit on your site.  If the two are close, you may have periodic overages which will cause sporadic problems.  Also make sure your Apache and MySQL are well tuned, as poor tuning can cause process stacking during cache clears, which can avalanche into a mess.