Make sure that you really have the line:
var buildings[300];

and no var or any other object that is named "buildings" too.

This code is working perfectly for me:
Code:

---

var buildings[300];



function save_array()
{
	var fhandle;
	var i;
	
	fhandle = file_open_write("save.txt");
	i = 0;
	
	while(i < 100)
	{
		file_var_write(fhandle,buildings[0*100 + i]);
		file_var_write(fhandle,buildings[1*100 + i]);
		file_var_write(fhandle,buildings[2*100 + i]);
		
		i += 1;
	}
	
	file_close(fhandle);
	
//	error("Array saved");
}

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