Don't know if this applys to your cassette, but here is what I finally figured out about mine.
On the side away from the tape in the center are two latching pivots that latch into the tape to keep it from turning when out of the machine. They have springs that keep little teeth engaged into the tape wheels. There is a third pivot that sits below the first two, with a flat that sits over a hole in the bottom of the housing and two little tabs that sit against the two latching pivots. When the tape goes into the machine, it goes in and down, and when it goes down it goes over a pin that comes up throught the aforementioned hole, pushes up on the flat on the third pivot. This rotates the pivot so that the two little tabs push on the other two pivots and disengage them from the tape.
For the door, on the bottom part of the case, on the right side, there is a pivot that is the latch mechanism. This is a small piece on the right side (when you are looking from behind the tape as though you were about to put it into the machine) that sits with its ends resting front to back, and a small button sticking out the right side of the tape. This button gets pushed in when you insert the tape to open the door on the front of the tape. There is a small shaft that is in the center part of this latch that stick out towards the back of the tape and just ends. There is a small spring that goes on this shaft, and the short end of the spring fits begind a little tab that sticks out towards left and is on the latch below the shaft. Once the spring is in place, take the long end (which will be sticking up) and push it down to the left (still working from behind, as though you were sticking the tape into a tape machine in front of you) and tuck it into the lower part of the case. There is a small indent that it will sit in that is in the lower part of the case. This should rotate the small button out through the right side of the case.
There should be one more spring that goes on the right side of the door (same side as I described the right side of the case above) on the pivot shaft of the door. There is a slot in the pivot shaft, and the spring has one end sticking out from the coil, and the other end sticking end. The part that sticks in slides over the shaft and into the slot. If you have it properly positioned, the part of the spring that sticks out will be sticking up (with the door sitting as thought closed on the tape case). Take the long end of the spring and tuck it under the lip of the tape door. On my tape door there was a little slot on the under side of the door to hold the end of the spring. Take the top of the case and put the left hinge shaft into the hole, and then slide the case under the lip of the door and over the spring (works like a charm, trust me). Then just set the case top carefully down on the case bottom, and you are done. Oh, but before you put the case top on, be sure all of the rollers and slides (one on each side in my case, and the one on the right was a steel pin with a nylon roller, and on the left was just a steel pin).
Good Luck
Anne Johnson, P.E., November 2006