Have gotten this error a couple of games when clicking on things to try and turn buildings on and off, a slow process, but I know they're working on that. Anyway, found the error inn a log file. Here is a paste of one of them.
NullReferenceException: Object reference not set to an instance of an object
at HUDInfoBuilder.buildToggleOffInfo () [0x00000] in <filename unknown>:0
at HUDInfoBuilder.guiGetObjectCostInfo () [0x00000] in <filename unknown>:0
at HUDInfoBuilder.buildGameMouseover () [0x00000] in <filename unknown>:0
at HUDListener.UpdateUI () [0x00000] in <filename unknown>:0
at HUDListener.Update () [0x00000] in <filename unknown>:0