BMW Repair: Coolent, coolant tank, coolant level

Question
We recently had the head gaskets replaced on our 1994 325ic BMW and the head shaved down b/c it was warped.  We also had the thermostate replaced because it was running hot.  It has been about 2 weeks since it was fixed and now all of a sudden when I turn the car off the computer tells me to check coolent level, but the coolant is fine and it is not running hot.  This is what was happening before we took it in to have the gaskets and thermostate replaced.  We are about to go on a long trip and I want to make sure it'll be okay to drive and won't start overheating on us again.  Thanks.  

Answer
The coolant level sensor depicts is the amount of coolant in the system.  Check the coolant tank, is it at the correct level? if so, the gauge or wire is causeing the computer to get a false reading of how much coolant is in the tank.
If the coolant level IS low, it's possible that the new head gasket was not installed correctly causeing the engine to burn the coolant again.  If they resurfaced the head only and did not check the blocks warpage or forgot to torque the bolts in the correct sequence, the gasket could be leaking.  See how much coolant it eats in a specified time, if it's noticeable, go talk with your mechanic.
-cheers