BUILD FAILED Unable to delete file hsqldb.out

Process Explorer shows you information about which handles and DLLs processes have opened or loaded.

• Download Process Explorer from Microsoft site and run the program.
• Click the Find menu, and choose Find Handle or DLL...
• Type the file name (name of the file which is locked by some process.)
• After typing the search phrase, click the Search button

You should see the list of applications which are accessing the file.