Peasant can't build towers after change

Hi, i am working on a Tower Defense map and i have a Peasant who can build towers however, when i change some value's in this unit (Invulnerable in Abilities Normal for example) the Peasant can build a tower but the tower got stuck at [0/200] and could not be finished, what i am doing wrong?

Made a screenshot to make it clear :

Did you delete its repair ability? Human peons place structures and then 'repair' them to full HP.

Your right! i deleted the repair ability. i thought the towers are invulnerable, there is no need to repair. repair does not make sence but it worked. thanks!

Each of the races have a different method of construction. If you want a non-attended structure creation then base your builder on the undead acolyte.