Here it is:

Warning: Warning: there are two 'Page' files both containing the same class: '/home/content/s/i/s/sistematisa/html/silverstripe/tutorial/code/Page.php' and '/home/content/s/i/s/sistematisa/html/silverstripe/mysite/code/Page.php'. This might mean that the wrong code is being used. in /home/content/s/i/s/sistematisa/html/silverstripe/sapphire/core/ManifestBuilder.php on line 253

it has appeared after clearing the cache (silverstripe's) for a few moments before refreshing, and in the CMS a few times already.

thanks for any help,
by the way i'm learning to develop themes, the way is done is simple enough for me to go and give it a try! , keep up the quality yet easy to adapt work!