Error 1901. Error attempting to read from the source...

Hi, anyone come across this before?

Trying to install SyncbackSE V5.20 and I get the Error..

Error 1901. Error attempting to read from the source installation database: C:\Windows\Installer\[randomcode].msi

I've disabled Anti-Virus (Kaspersky), and disabled and re-enabled UAC, run it as domain admin, nothing working so far.

I've downloaded and installed SyncbackSE v6 as a test and that installed fine, then re-tried V5 and get same error.

Any help appreciated.

Thanks