I just recently got the pmdg 737. I have done the first tutorial flight only two times now. On the 2nd time I did the first tutorial I got the message saying nav out of date on the fmc. I just cleared it out. But I am not sure if this is gonna effect future flights? Thanks.

Nav data are constantly updated, usually one cycle a month. You can go there to subscript your navdata cycles: www.navigraph.com