Did u read the firearms page??
It says:
Blank Guns, replica or imitation, PAINTBALL GUNS and "airsoft" guns MAY be listed provided that:
.the item does not, and cannot be readily altered to shoot a projectile(except paintball or airsoft guns)
.the reciever is not a firearm classified by law...
Check what you wrote again...see if theirs any words that might have prevented it..Other than that it doesnt look like ebay changed their policies so just try to list it again and see what happens...Hope that helps...Are there any laws in your area that classifies your marker as a firearm???