My first thoughts were hauling queueueues. Check the job list to see if any of the "to food stockpile" jobs mention seeds and are as yet unassigned. If there aren't any, and you don't have a set of other unassigned haulings, then are you surer you have Food Hauling enabled on dwarves who aren't busy on other tasks? If you have (moreover, other foodstuffs are being freely hauled) then the other things as schussel mentioned, indeed.
If you're really stuck, it might be worth designating all the stray seeds as Dumpable, see if they get Refuse Hauled to your garbage site. If they do move, then there's no access problems (and you have enough Refuse Haulers, obviously). Then unForbid them and see if they get transferred into theseed stockpile. Which they might not, if there's some other issue at play, but at least that batch of seeds isn't littering the halls any more, right?
(Extremely unlikely possibility: They've been reserved for planting, by farmers who are slovenly in doing so. Similar to how stones designated for constructions won't be picked up and stored in the appropriate stockpile (even though it might save time to move them there while the mason gets her act together)... But I don't think it'll be this unless you have an awful lot of fields and counting each and every "next seed" for each field as a job adds up to all those littering your site. I know it won't be quite the same as masonry building assignments, but I'm dredging my imagination for a reason here.
)
Ummm, just seen:
yes, that's the only one seed stockpile, other food sontains no seeds, forbidden there. and seeds are not forbidden, they just lay around. If I make another pile for seeds, they quick fill each place with single seed. A lot of empty barrels in sockpile, few of them reserved...
(Barrels in the sock pile?
Sorry, too good to resist!)
If the other seed pile takes seeds, albeit singly, is there a pathing/burrowing issue at hand? Seeds can be (and are being) taken to the other, but no the first. Barrels (which I think only take bags of seeds, anyway, do you have spare bags?) may not be able to get to the second. If I'm reading that right.