have a 2006 mercury montigo with a remote start and it won't work if the temperature gets below 30 degrees, any ideas on what it might be that's causing this problem

At this same temperature > Does the engine start ok when using conventional methods?

Your responses indicate that the remote start is aftermarket (not a factory option) so diagnosis could be tough if you don't have the documents to tell you the required parameters for starting. Since 2 systems do the same thing, it might be a default setting in the way it operates. Many factory systems will not allow remote starting if the battery voltage is below a certain amount. Battery voltage and amperage fall in cold weather so that could be your issue. If you have the manufacturer and model information, you may want to send an email to them for support.