Shift Override - GS400 gear shift stuck

[OwnerLexus_GS400]

I'm having an issue with my 99 Lexus GS400. I was leaving work on Friday, started my car and it would not shift into Reverse. I had to use the override to get home. I can only get the car into Drive now by using the override. All brake lights are working. Once in Drive, the car will shift into Neutral but cannot go into Reverse or Park without the override. How serious could this be, should I not drive it at all? I'm not in a position to get it fixed or looked at for another couple of weeks and I have some family members in a panic because I am using the override. Any advice here would be appreciated. 

[Exhaustgases]

I know of a Subaru that's been using it for 4 plus years now. And a Gen 1 LS400 that's going on a year.  Likely a switch or solenoid not working.

And that's what the override button is for, so when the automatic system messes up you can still drive it.