I see what cause of your problem, in file Base.class.php, there is a function called createParameterObject,
It is written as:
function createParameterObject($param, $path='', $type='menu') {
if(defined( '_JEXEC' )) return new JParameter($param, $path);
else return new mosParameters($param, $path, $type);
}
In this function, there are 2 choices to create it.
The first choice is used for joomla 1.5 with code:
if(defined( '_JEXEC' )) return new JParameter($param, $path);
end the second is used for joomla1.0 with code:
else return new mosParameters($param, $path, $type);
Normally, the second must be choosen (your site is joomla1.0) but cause of some problem
(I’m not sure what the problem is) the first is choosen.
It is waste much time to find what is cause, but you can solve this problem temporary by changging this function as:
function createParameterObject($param, $path='', $type='menu') {
return new mosParameters($param, $path, $type);
}
And change other functions as similar way.