If you see the error message access error after submitting a form this is an indication that the recipient group linked to this form has been deleted. When creating the form a recipient group must be assigned to it. If this group is deleted at a later point the data entered into the form can no longer be processed. You can solve this issue by a doing the following:
Begin by accessing the overview of all forms in the main menu under [Forms].
For every form you will see the assigned recipient group in one of the columns. If the group has been deleted you will see the note group deleted. You do not need to create the form completely new. Instead you can copy an existing form and assign it to the correct group:
Please note that some of the database fields for the form will need to be reassigned to the recipient group connected to this form. Open the form and check the settings under [Contents] > [Signup form].
After finalizing the copy you need to exchange the source code on your website with the code from the new form or respectively reassign the form e.g. in Wordpress/Typo3/Joomla.