According to a previous poster, there'* an internal transmission seal that not working properly and seems to be temperature sensitive. This prevents the car from going into gear.
I have a 92 SSEI with 141,000 miles and have the same problem. Parked in the garage and when the temperature goes below 50 degrees, I shift into reverse and nothing happens. A poster in the above thread suggests quickly shifting into first gear and then back to reverse.
What I found to work well is to start the car up and let it idle for 30 seconds or so. Shift into reverse and see if transmission engages. If it doesn't, shift it back into park and "blip" the throttle to 2500 rpm (quickly). Reverse or drive should engage.
This has worked for me so far...
92' SSEI/141,000 miles