Guild Wars 2

Sometimes in keeps, some of the upgrades, personnel in particular, are locked for some reason, and are unable to be bought. Does anyone know why this is, or how to fix it?

There are two kinds of upgrades — ones which instantly use supply in depot and ones which use it gradually. If an upgrade is locked it must be bought all-at-once and there isn’t sufficient supply in depot. Additionally, you can order two upgrades at once by getting one of each type (i.e. 2nd worker and Reinforced Walls).