It keeps going out after 5 mi.
I would check with your local fireplace company. It isn't something you want to mess with.
Check with your gas company. It sounds like it may need a thermal couple. I wouldn't try to deal with the problem myself. Gas can be dangerous.
It happened to us once. Assuming you have a remote starter, try checking the batteries in the "signal receiver box" near the logs. Not sure what to call it... Let us know if it worked.