Sorry to have abandoned the thread.
1. I know what a PHP warning is, the problem is that the code is still broken and as was pointed out prevents users from signing up.
2. There are lists selected when the error pops up.
It’s a moot point now. We’ve moved on.
Thank you. I think I am having a permissions issue on my site. Can you tell me where in the directory structure your plugin creates the csv file to be downloaded?
I just had the same problem, and I’m on a RackSpace cloud server w/ 256 MB RAM. I’m the only one accessing the site (dev, not production). Is this normal?
