I haven't used OSTUBE before, but I'd say removing the "__" won't help you.
You should be able to find a line somewhere that says something like:
$varName = new simpleuploader($var);
($varName and $var are just examples)
The problem seems like it would be with whatever you have where I've put $var.
I will try and find a copy of OSTUBE so I can help further
Edit: Just noticed this on the osTube website:
"
Not to modify the software's source code (especially applies to all PHP files)", so I would assume you shouldn't have to edit the PHP files to fix whatever is going wrong here... (assuming you're using the community edition)