Actually that form action uses Jomsocial Croute router so it should find the itemid on its own.
Make sure you have at least one menu Item pointing to
index.php?option=com_community&view=profile
Do you have a third party sef manager ?
If so think about disabling it for jomsocial urls
- Need help? Post the URL of the related page (eventualy as confidential info), it will help solve your issue faster.
- An error, notice or warning? report the exact message including the line number
- If you get a white page , enable error reporting and / or check your server error logs.