For this year, it appears to be fairly common for either the iginition key or the shift lock switch to fail. I've heard than of the two, the shift switch is much easier to replace. On mine, I had the ignition key go. Sounds like you might just need to replace the transmission lock neutral switch.

I'm having the exact same problem with my 1990 soft top. I'd be interested in hearing the fix. Mine just started the slow deck openning this summer. I guess it probably deserves a little care after 15 years.