file upload warning

hi i am using great real estate plugin there they asked to activate the some plugin, in that wp-downloadmanager plugin also i using when i tried to upload pdf file but getting this warnings unable to access means ??
i am having the file folder in that path but??

Warning: move_uploaded_file() [function.move-uploaded-file]: Unable to access /home/qiantum/public_html/wp-content/files/LA_BAHIA_PIB_Unbranded.pdf in /home/quantumi/public_html/wp-content/plugins/wp-downloadmanager/download-add.php on line 57