System calls Error in PHP

[mjm7867]

I am calling system("clamscan $tmp_file"), and on error_log it says:

ERROR: Can't access file /tmp/phpUIUJil
/tmp/phpUIUJil: Permission denied

so i checked the permissions, and what i did was to put a infinite loop to keep that tmp file in the tmp directory and tried to scan it, and it worked, but for some reason when i do it through php it says permission denied.

Help please!
Thanks in advance.

[mjm7867]

Same guy who asked the question, to give you guys more background:

first i m putting

$tmp_file = $_FILES['uploadedfile']['tmp_name'];
$result = exec("clamscan $tmp_file");
echo $result;

-------------Error_log------------------
mention earlier can't access.... permission denied......