Fatal error: allowed memory

Hello,
I’ve been using the jetpack plugin for a short time, and in the last days I’ve noticed this error at the end of my page:
Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 18874435 bytes) in /public_html/wp-includes/wp-db.php on line 1040
It doesn’t happen in every post of the blog, only in the last published, even if they contain only simple text.
When I deactivate the jetpack plugin it stops giving me this error, I’ve tried to reinstall it, also via ftp, and it still gives me that error.
When I deactivate the jetpack plugin it works fine, once it is activated I get the error, even if no modules of the jetpack are activated and if I haven’t even linked it to my wordpress account.
I was using the last 3.9 wordpress release, now I’ve updated to wordpress 4 but nothing changed.
The website is http://www.cursdecatala.com/, if you search on google “site:www.cursdecatala.com 1033” you will see all the pages that are giving me that error when I have the jetpack plugin activated.

It gives me the error in the wordpress file wp-db.php, line 1033 in wp 3.9.2, line 1040 in wp 4.0, the line is the one in bold:

function _real_escape( $string ) {
if ( $this->dbh ) {
if ( $this->use_mysqli ) {
return mysqli_real_escape_string( $this->dbh, $string );
} else {
return mysql_real_escape_string( $string, $this->dbh );
}
}

$class = get_class( $this );
_doing_it_wrong( $class, “$class must set a database connection for use with escaping.”, E_USER_NOTICE );
return addslashes( $string );
}

If anyone has any suggestion (possibly not to increase php memory, I would prefer to avoid to do that, it would be just a workaround), I’d be glad to hear.

Thanks a lot,
Claudio

https://wordpress.org/plugins/jetpack/