TYPO3 Core

As I said before it's the very same bug as described at https://forge.typo3.org/issues/71436#note-19 (I'm Jeff's workmate). There are no extensions involved, just a simple custom plugin with the default tt_content fields. The flexform configuration is this one:

<T3DataStructure>
    <meta>
        <langDisable>1</langDisable>
    </meta>
    <sheets>
        <main>
            <ROOT>
                <TCEforms>
                    <sheetTitle>LLL:EXT:tw_content/Resources/Private/Language/locallang_db.xlf:tx_twcontent_plugin.tab</sheetTitle>
                </TCEforms>
                <el>
                    <settings.elements>
                        <TCEforms>
                            <label>LLL:EXT:tw_content/Resources/Private/Language/locallang_db.xlf:tx_twcontent_plugin.settings.elements</label>
                            <config>
                                <type>inline</type>
                                <foreign_table>tx_twcontent_domain_model_icontile</foreign_table>
                                <foreign_table_where> AND tx_twcontent_domain_model_icontile.sys_language_uid IN (-1, 0) AND tx_twcontent_domain_model_icontile.hidden = 0 AND tx_twcontent_domain_model_icontile.deleted = 0 ORDER BY tx_twcontent_domain_model_icontile.description </foreign_table_where>
                                <foreign_sortby>sorting</foreign_sortby>
                                <foreign_record_defaults>
                                    <record_type>0</record_type>
                                </foreign_record_defaults>
                                <minitems>0</minitems>
                                <maxitems>99</maxitems>
                                <appearance>
                                    <useSortable>1</useSortable>
                                    <collapseAll>1</collapseAll>
                                </appearance>
                                <behaviour>
                                    <enableCascadingDelete>1</enableCascadingDelete>
                                </behaviour>
                            </config>
                        </TCEforms>
                    </settings.elements>
                </el>
            </ROOT>
        </main>
    </sheets>
</T3DataStructure>

... but it could probably even be reduced to some very basic setting. The error log says:

[15-Dec-2015 16:25:27 Europe/Berlin] http://xxx.tollwerk.de/ - Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1446996319: Configuration retrieved from FlexForm is incomplete or not of type "inline". | UnexpectedValueException thrown in file /www/htdocs/typo3/typo3_src-7.6.1/typo3/sysext/backend/Classes/Controller/FormInlineAjaxController.php in line 855. Requested URL: http://xxx.tollwerk.de/typo3/index.php?ajaxID=%2Fajax%2Frecord%2Finline%2Fcreate&ajaxToken=2716932dce5e3dbdc30fd75cd01bb19f524fcb17

Unfortunately the issue is keeping us from upgrading three otherwise totally 7.6 ready installations as it renders backend editing at least partially unusable.

Sorry, I just realise that the configuration example provided doesn't involve a FAL record as advertised. We experience the very same problem with any type of inline record, however. The error messages apply to FAL records as well.

Alright. I'll talk to Jeff tomorrow. I'm pretty sure he either overlooked your advise or it didn't work. We'll find out tomorrow. Thanks so far. :)

<type>array</type> does the trick, sorry for not checking this earlier!