This seat requires a key (the end tail of the adjuster strap) to be inserted into the base in order to remove the seat. The key was inserted, the lock was depressed, and I still could not remove the seat from its base. My husband and I managed to force it off of the base, then discovered that the manual (appropriately stored in the slot directly below the lock) had gotten wet due to snow coming off of our preschoolers boots. Water must have traveled down the base and collected on the manual — which then swelled up and got stuck in the unlocking mechanism, forcing it to remain unlocked, but not enough to release the seat from the base. It was difficult to remove the manual, and pieces of paper remained trapped in the locking mechanism. We needed to remove them with toothpicks and a butter knife, before we were able to get the lock to re engage and the key to work once more. Once again — manual was stored appropriately. Seat was never saturated and had no spills on it — but manual was soaked and covered in dirt. We assume it mustve been from her shs (she still rearfaces) as it couldnt have been anything else.