Exact same issue
Our product insert page uses both "insert record" and "insert multiple records" (for multiple categories). The products insert correctly, but does not redirect to products_Results.php.
We get error message:
Warning: Cannot modify header information - headers already sent by (output started at /home2/ahsafety/public_html/admin/products_Insert.php:47) in /home2/ahsafety/public_html/admin/products_Insert.php on line 426
Line 426 is multiple insert: