weird error - failed to open stream - .module file in theme path? I am just editing empty template, creating regions and so on. After I first time cleared cache weird error started to appear at every cache clearing: 


  Warning: include_once(C:\xampp\htdocs\hkmzvolen/sites/all/themes/activit/activit.module):
  failed to open stream: No such file or directory v
  _theme_process_registry() (riadok 565 z C:\xampp\htdocs\hkmzvolen\includes\theme.inc).
  
  Warning: include_once(): Failed opening
  'C:\xampp\htdocs\hkmzvolen/sites/all/themes/activit/activit.module'
  for inclusion (include_path='.;C:\xampp\php\PEAR') v
  _theme_process_registry() (riadok 565 z C:\xampp\htdocs\hkmzvolen\includes\theme.inc).


It is trying to include activit.module from theme folder and not from module folder. There are a custom module and custom theme with the same name - activit. But there is no any activit.module file in theme directory nor I am including the file anywhere in my code.

Why is drupal trying to include this nonexisting file from my theme path?
There are a custom module and custom theme with the same name - activit


That's what causes the problem. Module and theme names need to be unique amongst one another. Drupal doesn't support duplicate names, and weird things can happen if you go against that.

See Module/theme name collision for more information.