Separate names with a comma.
Is the Core gone from your inventory?
Any error message?
Please bear with me labling this as "not a bug". As Germanicus said, there is nothing we can currently do to avoid a situation like this. :(
I am afraid this is a known issue - as said earlier we aim to have missions for Colonists anytime soon .. but I am afraid we are not there yet....
/added for 1.5.5
Is chapter 5 completed?