You have to be speedy to be able to finish this segment of the level you're having trouble with.
You have to hit the switches in the correct order and you have to be sufficently quick (but not too quick) in order to hit all four switches. Once you satisfy the conditions, you will be able to move on to the next segment of the level.
If you continue to have trouble, I will try and post a replay of this level including all of the segments (it has been so long, I've lost a lot of progress and will need to reach this level again before I can make a replay).
I think this is the first time I've heard of this problem for this level. Other common problems include Mehdi 17 and Mehdi 13. In fact Mehdi 17 is one of the hardest levels 1.4 has to offer.
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