I've recently moved from [Windows 2003-32 bit, IIS 6 .NET 2.0] to [Windows 2008-64 bit, IIS 7 .NET 2.0].
Everything seems to be working fine except from the HTTP 500 error I am getting periodically and I also get timeouts in my database MSSQL 2005-randomly and on any on random stored procedures (DB is optimized and working fine-all stored procedures are working '0s' on the sql).
Any ideas how to resolve this error HTTP 500 error?
Work out what the error is for starters.
HTTP 500 is a status code for a server error. You will need to find out the details first.
Start with disabling 'View Friendly HTTP Errors' in Internet Explorer.
You need to find out more details from the server log: which 500 error are you getting? And take a look at the event viewer.
By default IIS7 runs in the new "Integrated Pipeline" mode, in which your ASP.NET application is running as part of IIS itself rather than through an external ISAPI plug-in. You may find that switching to "classic mode" gives you better stability while you find where the problem really lies.
(It may well be that you have some unmanaged resource, like a database connection, that isn't properly disposed. Check too the memory usage of the application to make sure your sessions aren't leaking.)
First of all get error info. Error 500 is a common error for any unhandled error.
There are some common causes and concerning migration I'd try switching application pool to classical mode. If this helps, you need to migrate your web.config to support IIS7 pipeline (some info here).
Turn on exception details, else IIS will always serve you a stupid HTTP 500 with no details on your crash.
Turn it off once you have fixed the issue.