how to get 737-400 to 39,000 ft?

Hi all
trying the European pilot in-built flight, from London to Paris (or Milan, can't remember)...
Using the default 737-400 I can never get to the FL390 that the ATC keeps telling me to reach ("expedite your climb")... Then after 3 warnings it ditches me from IFR.
From the specs for the 737-400 I can see that it's max altitude should be 37,000ft. So is there a bug in the program or am I doing something wrong?
cheers
S
trying the European pilot in-built flight, from London to Paris (or Milan, can't remember)...
Using the default 737-400 I can never get to the FL390 that the ATC keeps telling me to reach ("expedite your climb")... Then after 3 warnings it ditches me from IFR.
From the specs for the 737-400 I can see that it's max altitude should be 37,000ft. So is there a bug in the program or am I doing something wrong?
cheers
S