I had this problem happen years ago but it has been so long i can't remember what the fix was. My trunk only opens through the button in the interior below the dash. The key inserted into the rear lock doesn't do it anymore. Any thoughts on what this could be? Thanks

 

There's a little micro switch that is activated by turning the key. It's either out of position or it's whacked.
I just installed a bulldog keyless entry instead of fixing mine - it's much easier.