I don't think I even saw that question.
While I'm not 100% certain of the answer, I imagine if these pecans are vacuum PACKAGED (as in, bought at a store in a factory-sealed bag) you shouldn't have a problem. But if these pecans were shelled by you and then put in a baggie, I don't think they will be allowed.
At Madrid Barajas airport I always buy a bunch of bags of almonds at the duty-free shops to take back and never have a problem but thesea are in factory-sealed bags.
And while not certain (I'm not even sure what "PECANS" is in Spanish - it's a kind of nut), I don't think they have pecans in Spain. Some Spanish friends came to the US to visit and they LOVED the Pecan Pie and if memory serves me well they had not had them before.
Saludos, MadridMan