To solve some issues (POST and GET troubles), try to set the LogLevel in debug mode.
Open /etc/apache2/apache2.conf file (for Debian installation) and modify the following line:
# # LogLevel: Control the number of messages logged to the error_log. # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. # LogLevel warn
to
# # LogLevel: Control the number of messages logged to the error_log. # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. # LogLevel debug
Restart the service when modified.