Known issues
The issues below could be problems with the script that have not been fixed yet or Google Docs issues that affect how the script performs. I try to fix everything I can on my end and offer work-arounds for everything else.
Issue with Google Docs: Sheet size
I've noticed that some spreadsheets will not let you add additional columns past a certain point. The size limit of on a Google spreadsheet is fairly large, up to 256 columns. Source:
http://docs.google.com/support/bin/answer.py?hl=en&answer=37603
The way I work around this is to create a spreadsheet outside of Google Docs, make sure it's less than 256 columns wide, and uploading it. This gets a bit annoying when you already have information loaded but I'm not seeing another way to deal with it.
Getting "Invalid Feed!" with a correct URL
This is a problem with your host settings. Some hosts are ok with changing these and some are not. Email the technical support group for your web host with this information (from here http://www.tubepress.net/url-file-access-is-disabled-in-the-server-configuration.html):