What needs to be done that custom files can be uploaded via User Interface Options? The error message seems to refer to expect a MIME type (?)
A few people reported this problem and we believe this is related to an OS package which contains mime types as you mentioned. Check for the existence of the OS package shared-mime-info.
If it is already installed, try copuing the attached png-def.xml file to /usr/share/mime. Then run the following command as root:
Please let me know if this does fix the problem
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