Answer
Work through this checklist: confirm client.war actually exists and isn't corrupted in the repository's server/apps/main directory; if a client.war already exists in the target instance's ear/main directory, remove it and retry the installation; verify the account running the installer actually has write privileges to that target directory (test this directly by manually copying the file there yourself); make sure the installer itself is being run as Administrator; and finally, restart the application server host to clear any lingering file locks that could be silently blocking the copy operation. A stuck-at-a-fixed-percentage copy step like this is very often a file-permission or file-lock issue on the target directory rather than a corrupted delivery package.