i try to use some of this free maps using a 7.0.10.3 client version and i only can see a lot of black holes and one map i think has seen better days xD. any know the reason?
 
Most custom maps also use custom art files (item/land art and terrain/texture art). If you don't have the custom art files to go along with the custom maps, you'll see vacant or non-existent tiles (black land tiles and/or Unused item tiles).

The uo-developer site does not offer item/land mul files along with the maps they have posted, so you're out of luck with those unless you fix the errors manually (its extremely time consuming, I've done it). Uo-pixel (Eri) however, DOES offer mul files with the maps posted there. You need to dl those mul's and either merge them with your client, or use them outright. I believe the mul files provided there are around a 7.0.7.1 client - perfectly stable.
 
Maybe a year and a half ago, I converted all of Eri's muls over to 7.0.23.1. I'll see if I can find them.
 
Back