check the following steps, I hope it will work:
1- go to your IIS and right cliick on the folder of your website and check the asp.net tab and insure that there is asp.net version as 2.0.5... . if it's not then you have to install asp.net again with this code: %systemroot%\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis.exe /i in the command prompt.
2- go to Inetpub folder and then wwwroot and right click on the folder of your website and in the security tab add the aspnet permission with full control permission.
3- go to web.config file and check this things: a) if you're going to work with sql server 2000 or 2005 be sure that the connection string are set correctly.
b) be sure that the <UseInstallWizard> value is set to false.
4- in your iis right click on your website forlder and check that in the property - directory tab - Execute permissions is set to Scripts and Executables.
5- in iis - your website folder - property - documents tab be sure that there is a default.aspx as enable default document on the top, if not you can add it mannualy by clicking on add button and typing "Default.aspx" and then transfering it to the top of the others.
regards,
Hooman