I've created a 320x320 pixels picture to try if making a tileset will work. The TilesetM.bmp file has transparent upper left corner, three couloured tiles and all the others are black. I did everything ok and when I pressed "BUILD" an Error Message appeared saying :

Error! Can't open file "D:\Mladen\Jazz Jackrabbit\Jazz Jackrabbit 2\Tiles\TilesetM.bmp"
Done - 0 successfull build(s), 1 error(s)

Does anyone else has already had this problem and does anyone know how can I solve it?

This is the tileset (I made it using photoshop) :



The corner is transparent (dunno why it appears white)