HELP Installed rblt tranny, but shifter won't go into Park

[singnsave]

Hi,
Car is 1995 S500. We just removed the old transmission due to the Reverse not engaging, and are in the process of replacing it with a rebuilt transmission purchased from Sun Valley Mercedes Dismantlers. However, once the transmission was replaced and we checked the Gear Shifter, the Shifter would not go into Park. It's like hitting a wall. Pulled the Shifter up and looked into the area but can't see anything obvious that may be causing this problem. Has anyone experienced this before, or does anybody have any idea what it could be? I've searched through the blogs and could only find info on Shifter not going out of Park. I don't know if that is similar, but all the other gears appear to engage ok. Thank you for your speedy replies....we're in the process of working on it now and if none of you have any suggestions it will have to be towed to a mercede$ repair $hop.
Thank you!
Barbara