Use FirstName and LastName (no spaces)

Here is a listing of Reserved Words

Access warns about some reserved words but not others.  It warns you when you use "Name" or "Text", but doesn't warn you if you use "Caption", "Height", "Width", etc., even though they are all common property names.  The user has to be vigilant even when Access doesn't give a warning.  Sometimes you can get by with reserved words, but sometimes you get conflicts.  And it may become VERY difficult (if not impossible) to have to rename fields down the road, as any developer can attest.  Naming fields (and tables) needs to be carefully done right from the start, in order to avoid conflicts and other side effects down the road.