cannot upload files in media

I am getting an error code when attempting to upload a pdf file to Media. The error is as follows:
failed to upload due to an error
Unable to create directory /var/www/vhosts/asuemotionlab.com/httpdocs/wp-content/uploads/2012/08. Is its parent directory writable by the server?

I’ve never had an issue uploading files before and have never come across this message. I saw a similar issue in the forum, but the solution given did not solve my problem. Please help!