What are the known conditions / causes for "Installation error." "Unable to complete installation. Please download the file again." ?
1. Internet connection lost during download and / or install.
SOLUTION : Retry.
2. Failed download persisting in Web cache.
SOLUTION: Open Web. Clear Cache. May be restart and retry.
3. What else? Please list anything you know with your solutions.
Not sure upon what device you are trying to install this application or whether free or paid for version. Have to say that the free one requires data connection so that it can bombard you with religious prayers, so one to be avoided!