Spells: Paralyzing Earth wearing off early

[fahdazz]

I am having problems with the Paralyzing Earth spell wearing off early on my 49 Necromancer. I am fighting bloodgill goblins in Lake of Ill Omen and using no pet and only the spells in the following order: Paralyzing Earth, Ignite Blood, and Asystole. Some mobs are breaking Paralyzing Earth within a tick or two. These seem to be green cons that used to con light blue. Am I doing something wrong? Any help would be appreciated.