Cannot find file to copy - Build failed

For my extension, I imported library and pasted in the lib folder, then I also mentioned the jar file in the build.xml and in the main extension, but when I compile it I get error that :

C:\Users\user\Desktop\MyExtensions\nEW\Encoder\appinventor-sources-master\appinventor\build.xml:46: The following error occurred while executing this line:
C:\Users\user\Desktop\MyExtensions\nEW\Encoder\appinventor-sources-master\appinventor\components\build.xml:173: Warning: Could not find file C:\Users\user\Desktop\MyExtensions\nEW\Encoder\appinventor-sources-master\appinventor\build\**********\**********-2.2.4.jar to copy.

Can anyone help me? Please?

@ewpatton Can you please help me?

see how it is done for examle for the twitter libraries
then do the same for your library