creating problems with coupons

when I create a coupon and active send, takes me to a blank page that reads:
Warning: strtolower() expects parameter 1 to be string, array given in /home2/shopingc/public_html/wp-includes/formatting.php on line 1488

Warning: Cannot modify header information – headers already sent by (output started at /home2/shopingc/public_html/wp-includes/formatting.php:1488) in /home2/shopingc/public_html/wp-includes/pluggable.php on line 1228

I also found in my cpanel a file named: error_log
When I want to test adding a venue, (like a client) I think my own and I am sent to a blank page, the URL appears normal but the page is blank, no way to add a place, as it should be.
Im really confused, thanks for all the help you can give me, Happy New Year