I've had this problem before and it makes me crazy. I'll start importing something, like clay or reeds, to make finished products and export them, but after a few years I'm unable to import the raw materials anymore. I have room in my storage yards, I have money, I have a good kingdom rating, Ra likes me--even blesses me with inspiring my trading partners to trade more!--I haven't lost any trade routes, NOTHING. Yet it won't import raw materials! Does anyone know how to fix this??? PLEEEEEEAAAAAASE???

One of the following has happened:
* The trade route was closed / under siege
* The trade quota was reached
* The import quota set either by you or by the Overseer has been reached.
* You have disabled importing of that item.

Other than that, there is no other reason for a trade partner to just "stop" selling goods without input.

None of the above--trade routes are all open, quotas read 0/2500, I have none of the items in my storage yards, and it's set to import 1600 clay and 800 reeds (I never trust the overseer to set things, he does weird stuff sometimes). Everything SHOULD work, but it doesn't import. It's a bug, I'm sure, I just wonder if anyone knows how to fix it?

I was about to add another possible cause before you posted :P

Do you have room to accept the goods? As in, is there a Storage Yard set to accept the goods? If not, that may be a cause. Other than that, there's something wrong with your install. I can assure you it's not a bug as others would've noticed it by now (and definitely many years ago if it was a bug)

I have the same problem. Then I realised that there were no employees working at the storage yards to take the items! so I built some houses near and it fixed the problem for a while, until it happened again. So check that they are all fully manned.

It seriously drives me up the wall, it's the same with exports too, even if the quotas are not reached, they don't buy my items. In one city I have 100's of thousands of flax. So much flax.