1) There is not 'power to the latch' - that is a sensor that tells the PTCM when the latch unlocks or locks, the latch is powered and operated hydraulically.
2) I understand there is an adjustment needed to set the 'closing' of the latch, this is detailed in the service manual, perhaps this is the answer, since you say it releases fine.
3) It is POSSIBLE that the central locking pump has a bad output on the lines to that latch, I doubt this, but it IS a possibility.

The 2008 service manual has a more detailed chapter on the convertible top system than the 2005 manual.