helpe, uploading problem!

[eluser]benyu[/eluser]
When i using upload library got a error:
The temporary folder is missing.

In fact i have set up "upload_tmp_dir" to 'C:\windows\temp' directory which has EveryOne full control permission!

Although i have tried setting "upload_tmp_dir" manual with ini_set function in upload.php file,but get no effective still!

runing env:
windows2003 + iis6 + rewrite_isap2 + php5.2.6

thanks!