In command line, go to the folder of your .NET Framework version that is specified in the error page. It should be the small text at the bottom. Now type aspnet_regiis -i and you should be good to go. If not, try aspnet_regiis -u and aspnet_regiis -i afterwards. If that doesn't work, then keep trying aspnet_regiis -i. It'll eventually work I guess.
This is for a WinXP SP3 system running IIS 5.1.