This is possiblt because you are running php 5.3.x+ and the HTML form being submitted has more than 1000 elements in it. The JEvents config can exceed this number. PHP 5.3 onwards has a default limit ot 1000 on form input variables.
To resolve this please add this to the bottom of your .htaccess file
# JEvents form submission issue
php_value max_input_vars = 2000
If the above does not cause an error on your site but the problem still persits you may have php suhosin install on your server so try:
php_value suhosin.post.max_vars = 2000
php_value request.max_vars = 2000
If that causes an error on your site then add this to your php.ini file
max_input_vars = 2000
If that does not work then you may have php suhosin installed on the server so try:
suhosin.post.max_vars : 2000
suhosin.request.max_vars : 2000
If you need more assistance with these settings please contact your hosting company