What does this error message mean?

Try changing the permissions on the wp-content directory to 766. If you still have problems, try 767, 775 or 777. Once your uploads are working, change the permissions on wp-content back to 755 again and check that everything still works OK.
http://codex.wordpress.org/Changing_File_Permissions

Inside your root domain folder.

No. It means looking in the folder that you installed WordPress into.

Then you may want to consider hiring someone to help you with this. There’s not a lot we can do from here.

Not besides what I already posted in your other thread:

See: http://directory.codepoet.com/

or post a job listing: http://jobs.wordpress.net/

But per the forum rules, we close posts on this topic – as they attract too much spam – http://codex.wordpress.org/Forum_Welcome#Offering_to_Pay