I got an error from b2evolution blog. That is "Got error 28 from storage engine". And then, I went to my website backed Joomla. I got this error again. Then I can prove that is not the error related with the b2evolution. And I did some google search, I found out that is a disk space problem. So, I did a job request to my hosting provider. I think they increased the quote, then the problem is solved.