ASP.NET 4.5 incompatibilities

When we were prepping new servers to run Windows 2012 and ASP.NET 4.5, a lot of our users asked if we were also going to upgrade the existing Windows 2008 servers to .NET 4.5, so they wouldn’t have to migrate to a new Windows 2012 server in order to use 4.5.

A couple of things stopped us from upgrading the Windows 2008 servers, primarily the fact that .NET 4.5 is an “in-place” upgrade, meaning there is no rollback to .NET 4.0 if things go wrong.

But what could possibly go wrong? Microsoft assures us that .NET 4.5 is “backward-compatible,” right? As it turns out, by “backward-compatible,” they mean, “pretty much not-at-all backward compatible.”

So we did not upgrade any existing servers to .NET 4.5. Instead we offered new Windows 2012/.NET 4.5 servers for new accounts and as a migration option for existing accounts. As it turns out, not upgrading the Windows 2008 servers was a good move, because what we’re seeing now are a lot of people who have hosts that did the upgrade on existing servers and killed their customer’s applications in the process.

Here are a few popular applications and their current .NET 4.5 issues:

• DotNetNuke has a known compatibility issue with ASP.NET 4.5 that requires switching the Trust Level to Full.
• NopCommerce version 2.6 uses a freeware component named FluentValidation that is not compatible with .NET 4.5 if you are using version 3.3 or prior. FluentValidation released version 3.4 which fixed the compatibility issue, which allowed NopCommerce to release a new version (2.65) that is compatible with .NET 4.5. If you are currently running NopCommerce, you should use the upgrade script found here before migrating your site to ASP.NET 4.5. Note: Our Web App Gallery installer has not been updated to install version 2.65.  This will be included in the next release of the Web App Gallery.
• Some users have reported issues with older versions of Telerik Reporting after upgrading to .NET 4.5 on their local machine. According to Telerik, the issue has been fixed with the latest update.

Those are some of the bigger names affected by changes in .NET 4.5, but we recommend thoroughly testing your site and all applications in a .NET 4.5 development environment before requesting to have your site moved to a new Windows 2012/IIS 8/.NET 4.5 server.

As you can see, you cannot assume that everything that worked in .NET 4.0 is going to work in 4.5.