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We are in the prgress of migrating our main webserver from windows 2003 to 2008 and we need to install .Net 4.0 All has been complete and the isntallation has worked fine.

Whenever we change an app pool to .net4 (In iis) and try to view that site, we get a 500 error. However nothing appears in the event viewer.

Can anyone advise what are the best steps to start debugging this?

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can you get more details about the 500 error? Either make sure local debugging is allowed, or take a look at the web server logs, hopefully they give you a sub-code and some text to go with the 500. – MattB Nov 11 '10 at 20:02
Matt, thats what I'm trying to get my hands on. I'll be honest, this is new to me so any direction would be great. – LiamB Nov 11 '10 at 20:20
@MattB All I can see in the log files is the GET Request. May I can increase the logging somehow? – LiamB Nov 11 '10 at 20:27
@MattB - Fixed thanks for your help, I managed to find the log files and a few posts behind. The user of the app pool didnt have rights on the files and folders of the website. I'f you would like to put your comment into an answer about where to find logs etc it would help others and I can mark as complete. Thanks! – LiamB Nov 11 '10 at 20:43
up vote 0 down vote accepted

If you look at the log files for your site, they should give you more information about the type of 500 error that is being thrown. (A sub-code and/or some related text).

For IIS7, the default log location is %SystemDrive%\inetpub\logs\LogFiles\<SiteID>. The site id is most easily obtained by going to the Sites level in IIS Manager and looking at the ID column. If you go to your site and click on the Logging button, you can find the actual path to your log files, minus the site id.

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Do you have the latest fixes and Service Packs installed? We released a hotfix for IIS to add support for .NET 4.0.

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