When installing the PDA client you get the following message:

This advertised application will not be installed because
it might be unsafe. Contact your administrator to change
the installation user interface option of the package to basic.

There's a problem with an existing version of the PDA client, first try to uninstall the PDA client manually via "Control Panel - Software".

If that doesn't work try to find the location of the setup.msi file, usually: 

C:\DOCUME~1\username\LOCALS~1\Temp\~~adtmp~

And go to START, RUN and type the following: MSIEXEC /X "path to the .MSI
file you want to uninstall" and click OK.