HTTP 1.1 500 Internal Server Error - Help!!

This fixed my problem too. I thought I was going to have to reload IIS and recreate all my virtual directories (and I have a ton on my development machine).

Here are those four magic lines (run at the Visual Studio.Net Command Line):
1) iisreset /stop
2) net user ASPNET /delete
3) aspnet_regiis -i
4) iisreset /start


Another Alternate Way

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The fix below is for Asp.net new web apps not opening and receiving the 'HTTP/1.1 500 Internal Server Error'
Check the following:
“My_Computer_Zone code group” value on the Web server? To achieve that, you should do the following:
- Go to “Administrative Tools”
- Open “Microsoft .Net 1.1 Configuration”
- In the new window, expand the “Runtime Security Policy”
- Expand “Machine”, then “Code Groups”, then “All_Code”.
- Right-Click on “My_Computer_Zone” and select properties.
- On the “Permission Set” tab, the selected value should be “Full Trust”
- If it is not, you should change the value to “Full Trust”.
- You can test again creating a new ASP.NET Web application
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