EZ Secret SMS Full Version install Error

I downloaded the trial version of EZ Secret SMS V2 from Handango and installed it on my HTC WM6.1 phone. This installed and seemed to work ok. I then quite satisfied with the product purchased the Full version with it’s registration key from Handango.

First I entered the registration key into the trial version but it did not work. So I then uninstalled the trial version and ran the Full install of EZ Secret SMS V2 again. But it does not install giving me a “Installation was unsuccessful. The program or setting cannot be installed because it does not have sufficient system permissions.” I tried again after a soft reset but I still cannot install and receive the same error message.

Please help me to get this software to work correctly as I have purchased the software and require that it be operational.
Many thanks, Robuk.

every one seems to have the same problem. Even when installation is successful , you get a 'invalid registration code' reply. There seems to be no support for this software anymore. I guess the developer does not even exist anbymore and the software is still being sold separately