On the off chance that anyone will read this on a weekend, I managed to accidentally create a recursive reference in a Custom Block and now our Composer organisation is locked. Keeps throwing up the same error about the recursive reference.
I've exported the org, deleted the rogue block and imported again, but the error is still there.
Cannot open any forms or view the custom types.
How do you unlock a Composer org?
You would still need that rouge block for re-importing back in to composer. However you would need to 'empty' that custom type, example below. (change the module name from 'xxx' to match your rouge block name. You should be able to see this block again in the Organisation Custom Types and you can then choose to edit or delete. Hope this helps.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><module name="xxx" category="Custom" description="" editable="true" extends="Block-Standard" label="Test Custom Block"> <content/></module>
Thanks you so much for this! Managed to fix it today using the method you suggested.
In the meantime, I did manage to get it to work by deleting anything related to that broken widget and importing it as a new organisation.