Error uploading image

Description

Steps to reproduce

1. Create a new block in an Alloy template site.
2. In the Assets pane, go to Media > For this block.
3. Click the upload files link.
4. Click the 'plus' button and select an image.
5. The status says 'failed', errorMessage: "Content type "ImageFile" is not allowed to be created under parent of content type "<blocktype_name>""
6. Drag and drop an image to the block.
7. Try the upload again on "For this block". Now, the upload works.