Thanks for all your kind replies!

I got it resolved.  I asked and paid for .NET 4 hosting and got .NET 2.0.  I had to hammer the host to get it and prove I had something other than .NET 4.  Quite frustrating.

Paul

IndigoTea,

I keep running into this error all the time with Arvixe when I install a new website to use .NET 4.0 hosting.  I can switch it over to .NET 4.0 Intergrated Pipeline mode, stop the server, upload mojoPortal (I downloaded the source from CodePlex and compiled myself), then start the website and I get the same error about "system.web.extensions".  The only way I can get it fixed is to contact support for them to set it to .NET 4.0 as the Website Panel software freaks out and won't let you change it.  This occurs on their flax server, for the site dallasmicro.net.

Hopefully they can make this more reliable by the time it comes for me to renew as it is very painful to get a new site up in a timely manor compared to other hosting companies I use.

Thanks,
Todd

Hi, 

Similar issue here as well, however I manage my own server. 

I believe that I have .net 4 installed on the server as I have the folder C:\Windows\Microsoft.NET\Framework\v4.0.30319 as well as v3.0 and V3.5

I have a mojoportal installation running on 3.5 and have now set up (on a different drive on the same server) a 4.0 installation.

This new installation gets the 500 internals sever error and when I go into IIS to look at bits such as ".NET Profile" I get the 

Error: The configuration section 'system.web.extensions' cannot be read because it is missing a section declaration

as mentioned previously. If I go to view the site in visual studio I get the message that the site is V2.0 and do I want to update to 3.5, which I quickly escape from.

Any suggestions on where to look to resolve this. I am a bit ignorant with regards to whether a server can run both .net 3.5 and 4.0 versions of mojoportal. Ideally I would like to run both and upgrade the 3.5 version later if possible.

Sometimes the answer is too easy. 

Not being a master of IIS, I was not too confident with what you meant by 

You need to use a .NET 4 application pool in order to make a site run under .NET 4.

But as with most things you have a look round and the answer is staring you in the face.

For those who are like me to and were a bit confused what to do, all you need to do is go to IIS

Select Application pools and find the application pool for the .NET 4.0 site. Select this and then edit basic settings. In there is a dropdown box for ".NET Framework version" which in my case was set to ".NET Framework 2.0", I changed this to ".NET Framework 4.0" and the site is fixed. So much more easier that I was expecting.

Many thanks Joe