What causes purple button for custom LHs?

[Shekwan]

When I mod in a custom LH, I'm getting a purple square sometimes instead of the LH button. Sometimes however it doesn't happen, and I'm using the exact same method.
Anyone know the causes of this purple square?

 

[Edgecrusher]

The purple squares = Civ4 cannot find the art file in the defined path

Just doublecheck the paths, sometimes an extra comma (or lack of one) is all it takes

 

[Shekwan]

Great, thanks for the help thats sorted.