Speaking of which, I got a new error message.
I added four tile groups from the TNO (Bioware Castle Exterior Tileset) to the tileset I am working on. The Arena, Archery Range, Jousting List and Jousting Stands. This time, when I load the area with the tileset, I get a blank error message.
The .mdl files have the correct tileset tag, and I also made sure that the same has been adjusted within the files. Another change I made was to replace the TNO grass bitmap with that of the tileset I am adding to. I did change the names to tileset_u##_##. I am not sure if the letter category has relevance?
I double checked the Set File. The Tile and Group Counts are correct, the tiles have the correct Models assigned, and the groups the correct tiles. The .wok files match the .mdl files in name.
The ITP file has the correct commands (RESREF - RESREF - Model Name and STRING - NAME - Group Name). They are also in the right place. List Main -> 2nd Element -> List List "Grass". The Arena was under the grass feature category before, and I moved it to the group category as I thought that might be the problem. Neither place I assign it makes a difference.
When it did not work, I ran them through the CM3. I have everything deactivated besides the Raise/Lower Tileset option, as I was unsure what the rest would do. Having run them through CM3 also did not get rid of the problem.
All of them are correctly displayed though, when I load them through the NWN Explorer.