Make sure you come to a complete stop before trying to change gears. Also, make sure that you feel the detent on the shifter and see that the cluster display shows the correct gear selected.
There's a tip on our FAQ (http://www.smartusainsider.com/faq#faq05).
Let us know if that helps.
This post is nearly 5 years old. Anyone tried to get smart USA to cover this problem recently? My '08 cabriolet has 60K miles and started having this issue several months ago - often won't shift into reverse and sometimes drive when cold but don't think it has been an issue yet after it warms up.
This is a commonly discussed issue w the early 451's. I have the same problem w my 2009, especially when it's cold. If you haven't already, read the postings on this subject on the SCOA site. From what I've determined, two things can cause this. One theory is the early 451's clutch disc would stick on the transmission input shaft. A newer design clutch disc and new lube would fix it. The second theory is the transmission shift motor needs to be re-lubed. There's a great YouTube video from a 450 owner that describes how to do that and I would recommend you start there cause it's a whole lot cheaper and faster than replacing the clutch disc. Also, when my 451 does this I put the shifter in manual mode then I push the shifter forward and then pull it back as if I was upshifting and then downshifting and this seems to reset the transmission computer and it learns which gear I'm in and I can drive away w no problems.
Our gear shift display is blinking so I took it to our local mechanic and he told us we need a computer update but he was not able to do and I had to call a dealer about it. I did and they told us we had to bring it to a dealer and not to drive it but to haul it there. We live 200+ miles from the closest dealer. I called 4 different dealers and only 1 told me we could chance driving it there. Our car is a 2012 and has 45,000 miles on it. It shifts OK and seem like nothing is wrong except the blinking shift light and the wrench is on display. It would cost a fortune in towing expense + what it would cost for a dealer to install a computer update. Any solutions??