Well false E-04 codes can of course sometimes show up on other "D" and three digit models but not really on your model, and E-04 on these ranges is usually associated with a problem in the tape drum or the ribbon connections to it. A possible reason for this happening is that the sensor that detects a tape is installed has maybe gone faulty, or that the ribbon connection to it is defective as this could cause your symptoms, the sensor by the way being mounted on a small pillar situated half way between the two tape spindles but biased towards the cassette opening flap, you can detect it by a small orangey/ brown ribbon cable running from its base ("if" I remember correctly!) should you see the cable try moving it slightly with your finger tip in case its not seated correctly. Just out of interest, as this problem only seems to happen when you install a tape I assume you have found this fault occurring with more than one of them? A final long shot, if you get it to start the loading procedure whilst its doing it hold the rewind button and see what the result is, does it instantly start rewinding? (or forwarding)