Other Monks may find the following useful.
Recently I was involved in installation a Perl application on a new PC. The Perl application read and wrote Excel spreadsheets.
The application was used a number of times to test the installation and to sort the problem of how Perl applications with arguments are registered under Windows 7 (many thanks to the Monks who helped with this).
All of a sudden an error message was given and the application stopped working! This was traced to Perl code associated with Excel handling functions.
This bit of code is used in several applications at various sites for a number of years without any problems.
In the middle of this testing the PC hostname had been changed and other ‘things’ had been done.
After sometime and with the usual angst it was found that Excel had not yet been registered on that PC.
You can guess the rest, when Excel was authorized all worked as it should!!