Apologies for doing this here, could not reach member otherwise:
@faj you need to delete a few messages before you can receive more, seems your inbox is full! The forum message system allows only limited storage of messages.
Also not to forget to empty the bin.
Indeed, that was the problem. It is a bit surprising that the error message does not mention the cause of the issue, only something about messages being unreadable because they are on hold, which makes perfect sense sense... once you know what that means. Thanks!