Try entering 0.00 for the fee amount. Can you also send the url to your site if that doesn’t work so I can look at it please.
I Have a similar problem:
After adding an attendee to the wait list:
Order Details:
WAIT LIST
Event Name / Total Cost:
Warning: number_format() expects parameter 1 to be double, string given in /home/content/15/11124615/html/wp-content/plugins/event-registration/public/evr_public-confirmation.php on line 191
Test Event:
You are on the waiting list.
This appears to be a bug.
I have experienced a problem sending attendee confirmation emails. I’m using WordPress 3.9.2 Event Registration 6.01.07. It appears that If I register 3 or 4 times that I never get all the confirmation emails. I’m not sure what might be causing this problem. Its not a show-stopper but more an annoyance. I also had to add a plugin WP-SMTP-MAIL-CONFIG to get the confirmation emails to work. I would like to some day donate but I keep encountering numerous little problems.
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http://www.colonialdentallab.com