Apologies if my question is completely stupid or I have missed something fundamental.
Version: 1.73
Installed OXPs: Realistic Shipyards, System Redux
System: Core2Duo 1.6ghz, 2gb ram, Go7300
I have enough cash, but seem to be unable to mount any lasers. I can buy other equipment fine.
When I choose a laser in "Ship Outfitting" and press return, time adjusts by 10 minutes, the cursor returns to the top of the list and the basic menu sound "pluk" happens. However, the laser is not mounted.

Obviously this is stopping me move on from basic cargo runs to hunting baddies. Now I have *ahem* altered the save file so I have a military laser up front, but would like to mount another laser on aft.
All help from more experienced pilots welcome.
As this is my first post, i would just like to say what an amazing game this is so far, and give my thanks to the programmers. I am an old player of space sims [Elite, FOFT, Warhead etc] so seeing such a beautiful galaxy and reliving old space adventures is great fun and nostalgia.
If anyone has any recommendations of any pretty or essential OXPs I would be grateful as well.