Orientation of parts - Be sure to check and re-check orientation of blue and gray connectors. If you are unclear of the orientation on one page, go to next page to see what hooks into the pieces in question - this will help you place them correctly.
Track pieces - Connectors should attach to the track pieces with a firm snap. This will happen each time if you are sure to have each track piece oriented as the page clearly shows before attaching the connectors. If your track pieces keep popping off after you have attached them to the main structure, it is likely you have not "snapped" the connectors onto the correct side of the track.
Chain - Your chain may occasionally get caught on the black Chain Guides. When this happens the chain will stop moving and you will hear the motor clicking. Simply re-position the Chain between the Guides to stop the problem.
Page 8 Step 16 - The Micro red connector contains 3 Micro purple rods - Be sure center Micro purple rod is snapped into the connection point just off center on the Micro red connector. If the purple rod is snapped into the center connection point it will cause the track to be to close to the Micro blue rod and the car will hit the Micro blue rod and stop.
Page 12, Step 31 - Although the light gray Micro connector with the Micro black rod is a new piece being added to the model it may look shaded like you have already added it - you have not. This is easy to miss.
Page 23, Step 52 - The Micro purple connector attached to the track is very strained until the next track section is added to the model - this is normal.
Page 37, Step 83 and 84 - If the chain seems too tight after it has been attached to the model, verify that you have used the correct number of links. Also be sure the Chain comes out above the red rod at the bottom and is running over the red rod with the silver spacers on it in the middle.