If you mean you cant land your troops as in it crashes as soon as you press the accept mission button when your skyranger is parked there the I have a solution.
Try downloading UFO from Home of the Underdog (link is around between 2-6 pages back i think). It should work fine but just with a few randon errors which cause the gane to shut down, but they seem to occur less as you play more.
Otherwise i dont really know the problem that much, it only seems to affect some users (me
).
And Lizard, earth's heavy weapons dont become obsolete quick, i mean late in the game i still use the autocannon with HE/AP rounds and they rocket launcher with large rockets.
I know the blaster bomb makes rockets pretty obsolete with thier improved range and firepower, but its great to just fire from A-B with a large rocket, also useful in terror misions when its not the best idea to blow up the whole building justincase civs are there.
The HE autocannon is usefull in base assaults and defence, they have a good explosive radius to blow up lots of enemies in the small corridors. Especially usefull against chyrsalids who seem to die in one hit.
What is really good though as ive said before are heavy lasers, they are cheap to produce and maintain, great accuracy and high damage, just give one to your best shot and you will reap the rewards of one hit-one kill.