There are many things that could have attributed to its degradation.
Having it out in open air for too long
Having it out in heat for too long
Exposing light to it for too long
Or it could just be weak L and you were lied to.
(A sad, but never ended posibility in the drug game)
In the future, choose a better item to drop the L on. Sugar cubes, marshmallows, or crackers work best (that is, if you dont want to get art paper for it [120lb], which would be best as sugar degrades faster)
The problem with sweet tarts, or any candy like it (pez come to mind) is that they're not all that absorbant, so it definitely takes longer to dry the LSD.
You dont need to keep them out for a while for them to dry. Ive found that keeping them out for only a few minutes will get them to where you want them to be, and then wrapping them in foil and double bagging them (getting as much air out as humanly possible [or, if you can, vacuum seal it]), and then sticking it (preferabbly in an amber vial) in the freezer or fridge. I suggest the fridge as theres less chance of getting any form of liquid in there.