The vaccine in Code of Honor was impossible to replicate, even though Dr. Crusher possessed a sample of the vaccine.
Not impossible to replicate, just unstable when replicated. Why that would be the case, beyond dramatic needs, is unclear.
The Child, replicating 512 special specimen containers required divert power from the warp engines into the replicator for two hours, the ship couldn't go to warp because of the replicator power requirements.
In other words, the replicator can require warp drive levels of power to make certain things.
Something I've never disputed. Some things may be more difficult to replicate than other things, like the vaccine samples in "Code of Honor", but I've not seen anything explicitly described as "impossible to replicate".
The genetronic replicator as described isn't a replicator in the usual meaning. According to the shows technical advisors, the replicator dematerializes base material, changes the material while in the matter stream, and then materializes the re-arranged item. All this happen relatively quickly.
Worf 's new spine is specifically refer to as being grown, plus by dialog growing the new spine takes approximately one hour and forty minutes.
Strickly speaking, Worf's new spine wasn't replicated.
Strictly speaking, it was replicated, as in a copy of Worf's spinal cord was made and used to replace his severed one. The fact that it took hours instead of seconds doesn't seem like anything worth quibbling over.
My take is that the replicator has problems with some complex compounds. That's why it could not make that drug. Air and water are fairly simply.
And maybe that's all that's ever encountered - problems with replication, not impossiblities. Maybe if Crusher took more time to work on the unstable replicated vaccine, she would have solved it. A deadline, with thousands of lives in peril, prevented her from bothering with the replicator when a natural stable source was nearby.
It's funny though that Neelix managed to live with holographic lungs for some time, but the replicator couldn't make one. I might guess that tissue compatibility might be a problem, so just replicating one from the database and installing it in Neelix might kill him. But I can't see why taking more time to clone some of Neelix's tissue and figuring out how to make a compatible lung couldn't be done. I wonder if the genetronic replicator was still in beta when Voyager was launched.
The "compositor" has to be made of something. There are over a hundred elements on the periodic table. Compounds are chemically bonded substances that contain two or more different elements."Beta-matrix compositors" are a piece of technology, not an element or compound
Thanks for the tip!

