Cannot install Lexmark productivity Centre for X4650 printer.

Cannot install Lexmark productivity Centre for X4650 model on Acer PC with Windows 7 Home Premium 64bit. The install routine keeps telling me to download .Net v2 from Microsoft. When I try to do this I'm informed that the .Net v2 (x64) software is already installed (which it is). I've downloaded the Windows 7 driver for the printer and reinstalled but I still get the same error.