The problem comes from the code
Joomla.submitform = function(task, form) {
if (typeof(form) === 'undefined') {
form = document.getElementById('adminForm');
}
if (typeof(task) !== 'undefined') {
form.task.value = task;
}
of the file media/system/js/core.js which throws the error below when clicking on a button :
core.js:24Uncaught TypeError: Cannot read property 'task' of null
But on our version of Joomla 1.7.0 (the official that we downloaded from joomla.org after the release) on which we tested HikaShop, we don't have that problem, simply because we don't have the same code in that file.
We actually have the code:
Joomla.submitform=function(a,b){if(typeof b==="undefined"&&(b=document.getElementById("adminForm"),!b))b=document.adminForm;if(typeof a!=="undefined")b.task.value=a;
So there are three possibilities here:
1. You installed an extension which changed that file
2. You changed that file yourself
3. You use a version 1.7.0 which is not the final version
If you use the original core.js file of the currently released 1.7.0 package instead of your current core.js file, that will solve the problem.