[Plugin: SimpleModal Contact Form (SMCF)] Uh oh… 404: Not Found (error message

Thanks for the great plugin! Unfortunately I am having some problems getting it to work, even after reading the documentation and doing some online searching. I keep getting that error message when I click send, and no email is sent.

I’m running WP 2.9.1, made some changes to the CSS and added an additional field (phone number), but other than that it’s un-modified.

In trying to solve the issue myself I found some limited info here: https://www.ericmmartin.com/projects/smcf_archive/ but that is for an older version of the plugin, and according to the comments that issue was fixed in newer releases. Any ideas?

https://www.ads-software.com/extend/plugins/simplemodal-contact-form-smcf/