For the first case, you need to have a single texture in that case. If the texture is too large, then there are other tricks that I know of, rather simple ones, that allow for getting rid of the seam, but it would take modifications of your textures and it may not work (I haven't tested it yet).

My version of 3D Game Studio only allow a maximun texture size of 256 by 256. If you exceed that it will crop off the rest and tile the first 256 by 256. I am not sure why but i guess it is used for saving memory purposes. Therefore I cannot use a single texture.

For the second case, you can resize blocks to use a larger texture. Either that, or use a model instead as model-only levels have tons of major advantages than levels made from blocks.

As memtioned, since large texture wont work, i proposed another solution; that is to use small blocks for large texture. An example would be using four 64 by 64 blocks for a 256 by 256 texture. This way the lines will not be solved but greatly reduced by at least 4 times. However, the downside is that everything will go pixilated during closeup, which will affect gameplay experience. Do you think this solution is good or there might be better ones?

For the third case, what I'm referring to is using the ent_create command in your script. If you ent_create entities that use this position where the gap is, odd things can happen.

I am not the programmer of the game, hence i am not sure if the programmer used the ent_create command. However, i am very sure that this is unlikely the cause because it is present during runtime in WED without script attached.

What edition do you have? 6.20.2 is an old version. I suggest updating it to the latest version, 6.40.5. It's a free update. Although this will unlikely fix the tiling issue, it can help to some extent.

I am using the 6.20.2 Professional Edition but i cannot update because i do not have the password.

Lastly, thanks alot for the help and concern ulillillia.