Photoshop :: How To Eliminate Lines Which Appear When Tile Repeated In CS6

I'm using photoshop cs6 to create textile designs, and occassionally, (it hasnt happened with every tile) when i change the image size of my tile e.g. from 15cm sq to 10cm sq, then try to repeat the tile it forms thin lines between the tiles?
 
heres the tile repeated after ive changed the image size and you can see the thin lines...when i zoom in on the tile edges where the line has formed it looks like this....almost as if theres empty pixels that can then be coloured in.

i dont think its a problem when creating the tile because before i changed the image size it repeated fine with no lines, its something thats happeneing when the image size is altered.