Here is a solution that work for us.
First check in the logs error if there something like this:
PHP Fatal error: Using $this when not in object context in libraries/joomla/filter/input.php on line 233, referer: http://yoursite/uddeim?task=new
In this case,
you have to edit the file /components/com_uddeim/uddeim.php
It use a class native of Joomla call JFilterInput Here is the problem. In the version of Joomla 3.5 you have to iniciate the class with the object, it isn´t static class. In this case use a method call clean(). So in the file uddeim.php you edit and force that dont use this method, is not necessary.
So you edit /components/com_uddeim/uddeim.php
Replace this in line 2668
if (class_exists('JFilterInput'))
$input = JFilterInput::clean($input, 'username');
else
$input = (string) preg_replace( '/[\x00-\x1F\x7F<>"\'%&]/', '', $input );
to:
// if (class_exists('JFilterInput')) {
if (false) {
// $input = JFilterInput::clean($input, 'username');
$input = new JFilterInput;
$input->clean($input, 'username');
}
else {
$input = (string) preg_replace( '/[\x00-\x1F\x7F<>"\'%&]/', '', $input );
}
let it commented the above code because of a change of version may be able to put it back as it was originally
And in the line 2835 approximately repeat the same.
good luck
