animate({ scrollLeft: '+=200'}) does not work but .scrollLeft(200) does?

animate({ scrollLeft: '+=200'}) does not work but .scrollLeft(200) does?

Hello,

I am trying to get the gallery on http://www.hotel-mutterhaus.de/-78 scrolling when clicking the previos/next buttons.

*Something* must be blocking it but despite twisting my head for well over an hour now I don't get it.

Fascinating is that while jQuery(".gllr>.cntnr").scrollLeft(200); works perfectly, a jQuery(".gllr>.cntnr").animate({scrollLeft: "+=200"}); does not work at all.

Using jQuery 1.4.2

Any suggestions?