Plugin creates an internal server error

For the last few days, when the contact form is filled out, it directs users to an internal server error page. At least a PDF with the contact form is submitted just fine, but having users hit an error page is obviously an issue. After combing through possible error issues, I figured out it has to do with this plugin. I tried to access the plugin settings within the admin panel, but it directs to the same internal server page. So I can’t even edit the settings. I disabled the plugin, tried filling out the form, and there is no longer an error page. I reenabled the plugin, filled out the form on the website, and no error page. But no PDF, since my PDF was deleted! I went into the plugin settings, created a PDF, filled out a test form, and was sent to an internal error page again.

HELP!! I really need a PDF to be attached to every contact form submission.

Also, as I mentioned, when the plugin is disabled and reenabled, my PDF settings are gone. This is a huge pain since the contact form is quite lengthy and took me a while to style just right. And now I have to completely recreate it.

Any advice to avoid these issues in the future would be much appreciated.