It takes some practise to make it easier.
First time I did it, I managed to 'rotate' the pins on the bottom of the seats, meaning that the ball inside of it wasn't coming out properly, hence preventing any lock-down. I corrected that with some prying and turning with a screwdriver (no need to force things, just compare some other pins to see what they should look like and match them)
But I assume you've removed your rear seat before and had no problems then.
Maybe lubrication then? Let the dealer decide, I guess, if still under warranty.
Cheers,
Edo
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(2003 Silver 1.4 Tdi Exclusive(SE), 95bhp/235Nm chiptuned by ABT, black interior, sport seats, heated mirrors, TomTom3 PDA Satnav, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)