Start your visual studio .net command prompt and do the following
1) type "aspnet_regiis -lv" (without the quotes), which tells you whatever asp.net versions you have in your com. The one with the (root) is the one you're using.
2) type "aspnet_regiis -ua" (without the quotes), this completely removes your asp.net in your com.
3) type "aspnet_regiis -i" (without the quotes), this reinstalls the asp.net.