Question : Error 1720 installing software for Shoretel Call manager

We just got a new phone system in our office (ip phones) and the desktop software will not install on a couple of computers.
Both computers are Vista SP2 (just like the others where the install worked fine) but am getting an error 1720 referring to the Windows Installer.
I haven't been able to find the correct Windows Installer for these machines, or else it isn't working correctly.  I tried to install 4.5 windows installer and it just kept telling me not enough disk space (which is completely not true).  So I searched for windows installer for Vista and wasn't able to find what I thought was the exact version, or any version I could get to work on these two machines.
Attached is the description of the error in Event Viewer

Answer : Error 1720 installing software for Shoretel Call manager

I found someone yesterday that knew how to edit the .msi file and that's what finally worked so I will close out this ticket.
Thanks for the info.