Thanks for the swift response.
I deleted the old plugin and downloaded again from the plugin directory (1.0)
I got this error on activation:
The plugin generated 17 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.
However, the header error noted previously is now gone.
It is conflicting with Super Cache in some way it seems, but even when I deactivate that plugin, it is not saving new team members.
The live site shows this error message at the top of the page with Super Cache activated:
Warning: Cannot modify header information - headers already sent by (output started at /xxxl/wp-content/plugins/flipping-team/flipping_team.php:109) in /xxx/wp-content/plugins/wp-super-cache/wp-cache-phase2.php on line 77