Uninstall microsoft silverlight 5 and downgrade to version 4

I recently installed the internet plugin silverlight 5 on my mac and I intend to make a complete uninstall. I ran all the steps required for this purpose and search every corner of OS if there would be some extra element forgotten. I found none and surprisingly, when I try to install the required version 4 by a program that i use, and does not supports version 5 installer, in the volume installation selection, it simply does not allow me, saying that the operation could not be completed because a newer version exists in the system... I have repaired the disk, preferences and manually uninstalled items from Frameworks folder but the problem remains. How can I get rid of this so i can install version 4? Someone can help me?

thanks, Hugo

iMac 2.66Ghz intel core 2 Duo, 4Gb 800hz DDR2 SDRAM

OS Lion