This quite common that mod_security is interfering the functions of your web applications. mod_security is installed and enabled by your web server admin but you can still disable it for your individual website using .htaccess file by following this tutorial.

Disable mod_security in .htaccess file

If you do not have one yet, an .htaccess file in the folder of your web application

To disable mod_security COMPLETELY, add the following line to the .htaccess file:

SecFilterEngine Off

OR, to disable HTTP POST scanning only, use the following instead:

SecFilterScanPOST Off

Save the file and test your web application to check whether disabling mod_security has solved your problem.

You should consider to try SecFilterScanPOST Off first, instead of disabling mod_security completely.