Android Question modify a old project

[jinyistudio]

I copy a old project and rename to a new project blueLT.
When I run it, It always give a complie error as attachied file. I don't know what it happen ???

 

[jinyistudio]

I try modify old package name form jylab.blueLT to tw.jylab.blueLT. the compile error Disappear,I don't know why ???

 

[Erel]

Hard to say without seeing the original project.