I am no expert but i can see that no one here to answer you, so I'll try
I had this problem before.. so:
Somewhere you load the testdata/alphamap.png i guess for sprite or something, and your environment (I'm using eclipse) cannot access this file.
What i did was, creating a folder in the project and linked it to the folder where my pictures in my computer are, so the project will have the images saved in side it and he can get to them.
NOTE: the path testdata/alphamap.png means the it should be YOURPROJECT/testdata/alphamap.png, which means the folder should be named testdata.
Hope i helped