I receive the same message than explained in this thread when I'm trying to restart apache2 :

 * Restarting web server apache2 [fail]

 * There are processes named 'apache2' running which do not match your pid file which are left untouched in the name of safety, Please review the situation by hand.

But the problem is that I don't have any file inside /var/run/apache2.
The command pidof apache2 returns :

1274

I don't know if it will help but here is the line in apache2.conf :

PidFile ${APACHE_PID_FILE}

And the one in envvars :

export APACHE_PID_FILE=/var/run/apache2/apache2$SUFFIX.pid

Should I manually create a .pid file inside /var/run/apache2 ?

Thank you very much !