Help, carrionswam doesn't work

In my map, the order "order unit to carrionswam a point" doesn't work.

Set Temploc = center of map area
Create a Caster at TempLoc facing xxx dergee
Add "carrionswam" to last created unit
Order last created unit to carrionswam (TempLoc offset by (100,100))

The Caster unit is created. But it seems ignore the order and doesn't move at all.
I am sure it has enough mana, and it has the skill, because I can use carrionswam manually after it's created.

Any one know how to solve this problem? Thanks.

I know this doesn't belong in in the site discussion.
Go to the trigger forum or better, wait for a mod to move this.

thanks , i have posted one there, please delete this