My hosting company said they did not what to do because it is strictly a matter of programming.
The problem occurred in a few hours after I tried to intoduce a language Pack in the Langs folder. There already exists a php file with that language and I've changed the content.. Translation worked but had some errors so I put back the original content.
The site worked perfectly after that but a few hours later appeared that message.
I do not know if this is the reason but this is the last thing I did before the problem occurs.
Thank you