Ant task : how to avoid re-executing the same task

Hi all, If you are in a hurry and want to help me too, the question is at paragraph 6, thanks. I use an task to import global properties for each ant script of a project. When debugging through the ant scripts I notice that each time the import statement goes through all of the import file.

Cannot copy due to null

I am getting a strange error: cannot copy due to null. Any ideas why this happens? Why is there no message? Log output below. Thanks! prepare-etc-test: [copy] Copying 1 file to J:\ops4j\projects\legacy\transit\core\handler\target\test [copy] Warning: Failed to copy J:\ops4j\proj