Question about upgrading units

[MMRegent]

Sometimes, when I attempt to upgrade a unit, it won't upgrade. Obviously, I am *not* referring to instances in which I lack the necessary gold, advancements, or strategic resources to do so.

Note that this does not always happen (Nor is the problem confined to any particular type of unit). I am not always unable to upgrade units - only sometimes. But when it happens, it happens like this - if I try to upgrade a single unit, nothing happens. If I hit 'Shift-U' to upgrade all units of that kind, say, for instance, a cannon to artillery - I will get a pop-up window from my military advisor saying that "We have not a single cannon that can be upgraded," despite me having several cannons.

I am a somewhat new Civ player, (I am currently playing my 5th Civ), but I know enough to know that my inability to figure this out is probably based on something more than just the basic knowledge I can find in the Civilopedia. Is this just a bug in the program, or am I overlooking something? Has anyone else had this program? I had this problem with Civ3 by itself, and still had it after I got PTW, and still had it even after I downloaded the 1.29f patch for PTW. Now that I have Conquests, it is still happening.

Much thanks to anyone who can shed light on the problem for me

 

[wilbill]

Units need to be in a city containing a barracks to upgrade. And the city needs to be connected to the necessary strategic resources (showing in the city view).
Welcome to CFC!

 

[Ahab]

I had an interesting thing happen to me in my current game related to upgrading/training units. I declared war and all the sudden couldn't train beyond archer/spearman. It took me a while to figure out that my only iron resource was connected to my mainland by harbor, but the only 'safe' sea route went through the territory of my enemy. Obvoius in retrospect, but it was a bit confusing when it happened.

 

[Raijer]

I'd agree with willbill... sounds like you don't have barracks, an improvement necessary for upgrades.

 

[silver spork]

I'm a long time civ2 player, but a relatively new civ3 player, and I had that same problem, and like wilbill and Raijer said, it ended up being lack of a barracks in that city.