If I am using a weapon that is rated medium range, does that mean I cannot use it from long range (therefore I must move to medium range to fire) or is the difficulty increased to be able to reach long range (difficulty or setback dice)?

Listed is the maximum range, I believe.

If you want to shoot further than this, check out the Sniper Shot (for shooty-shooty) and Strong Arm (for thrown weapons) talents.

I've long felt it might have been better to label that category as "Max Range" rather than "Range", because I find it confusing and I see it confuse others very often.

Especially when you have the skill listed right next to it. "Ranged [Light], Range: Medium".

Unless you're reading VERY carefully, it's easy to get confused.

Ok, max range. So medium range weapons cannot be used at long range. Makes sense.

But, as previously mentioned there are talents, and I believe weapon mods, that can extend the range.

I believe weapon mods, that can extend the range.

Yeah, Marksman Barrel.

Strange I forgot that one - my GM blew up my rifle (two Triumph) a couple of weeks ago.

Narrative wise, aim and effective stopping power become uncontrollable and therefore ineffective once you have exceeded max. Range. I'm not sure how you would narrate effective power of a blaster bolt, but given the description of how blasters work in the first place (they require some sort of propulsion in the weapon, as opposed to a true LASER), I don't see it as a huge problem to suspend disbelief.