This is usually related to the mechanism that connects the shifter to the ignition key and steering column. I've been working on the same issue, and 1 of 2 repairs seem to be the norm.
As a short term fix you should see if you can gently pry the shift interlock button upward with pliers or a pair of small screwdrivers. Obviously be careful of damage. On this same tack, especially if this is a short term fix, you can remove the center console cover and clean, lubricate, and generally tinker with the mechanism looking for dirt and debris.
If this isn't a fix then the key cylinder generally needs replacement. This is a dealer event, but not too costly for labor.
Avoid heavy key rings!!!
Try jiggling the steering wheel a little, press your brake pedal, and make sure your car is in PARK.
Type your answer here... BIG!
In the footwell, driver's side, behind the kneepad.
the tow capacity should be labeled on the inside door
check emc fuse and the fuse next to it
It's broke you idiot!
under the coin holder, under the ash tray ciao - Max
It is in the console near the parking break handle when it is pulled on, on the right side under a small access panel.
bad ignition switch - inside steering column
this is one of those problems where your tear down the colum and go from there.
Have browsed forums about a similar issue on a 1997 Volvo V70. One suggestion was that the throttle control valve might be stuck. I couldn't be bothered to fix it so I bought a new car instead. :)
Probably 1996 thru 1999 if it is going wagon to wagon.