Error Trying to Import Items and/or Metadata

I'm not 100% sure if this is a server issue or an Omeka issue so I'm posting my issue to both Help forums. Today we started receiving the following error message when attempting to upload files to our items:

File Upload: File 'file_0_' can't be written.

We have been able to upload items without this error prior to today. I attempted to upload both a PDF file and a JPG file and received the same error. In regards to non-images, I also had difficulty importing a CSV spreadsheet and had to log out and back in of the admin section of the program to get it to successfully import. The error message there was:

File 'csv_file' can't be written

I attempted to get around the issue by uploading all of the files to my Dropbox plugin folder and attaching items that way, but either it failed or the attached item had fatal errors (all files on their original drives have no errors and open correctly). Any ideas what might be the cause of the problem? Our Omeka installations are on Bluehost.

This sounds like a permissions problem on the server.

Make sure your user that's running Omeka (often the web server's user) has permissions to write to the server's temp directory and PHP's upload temp directory (set as upload_tmp_dir in php.ini).