The Skype updates in Patch My PC SCUP catalog uses the MSI based version of the Skype installer: http://www.skype.com/en/business. This MSI based installer may not change the MSI product code for incremental versions of Skype e.g. Skype 6.20.0.104 to Skype 6.21.0.104.

This would cause the Skype 6.21.0.104 to be detected as installed even if Skype 6.20.0.104 was installed. This would also cause an installation of Skype 6.21.0.104 to error out with code 1638 “Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs on the Control Panel.” if Skype 6.20.0.104 was installed.

As a workaround any incremental version of Skype that uses that same product code as a previous version will use a custom self-extractable .exe file (SFX installer). The SFX installer will use the same MSI installer released from Skype, but this installer will be called from a wrapper script (VBScript) that will uninstall the current version of Skype using the ProductCode prior to calling the new installer. This will allow the new installer to install successfully. This SFX installer will be signed by our code signing certificate.

This wrapper script will also create a log that can be reviewed for troubleshooting:

Location: %windir%\temp\PMPC_SkypeSetup_<Version>.msi_Install.log

Sample Log: