When you live on the bleeding edge, be prepared for a few nicks [Minor update to the Delay.Web.Helpers ASP.NET assembly download to avoid a NuGet packaging bug affecting Razor installs]
I had a surprise last week when coworker Bilal Aslam mentioned he was using my Delay.Web.Helpers assembly but wasn't able to install the 1.1.0 version with the ASP.NET Razor "_Admin" control panel. (Fortunately, the previous version (1.0.0) did install and had the functionality he needed, so he was using that one for the time being.) I quickly told Bilal he was crazy because I remembered testing with the NuGet plugin for Visual Studio and knew it installed successfully. At which point he demonstrated the problem for me - and I was forced to admit defeat.
Aside: Delay.Web.Helpers is a collection of ASP.NET web helpers that provide access to Amazon Simple Storage Service (S3) buckets and blobs as well as easy ways to create "data URIs". (And eventually more stuff as I get time to add it...)
Naturally, the first thing I did was to repeat my previous testing in Visual Studio - and it worked fine just like I remembered. So I tried with the Razor administration interface and it failed just like Bilal showed me: "System.InvalidOperationException: The 'schemaVersion' attribute is not declared.". Because the previous version (1.0.0) didn't have this problem, I was a little confused; I'd built everything from the same .nuspec file, so it wasn't clear why the Razor/1.1.0 scenario would be uniquely broken.
At that point, I contacted a couple folks on the NuGet team and got a quick answer: for some (short) period of time, the official version of nuget.exe created packages with a schemaVersion attribute on the package/metadata element of the embedded .nuspec file and the presence of this attribute causes the Razor install implementation to fail with the exception we were seeing. I'd created 1.0.0 with a good version of nuget.exe, but apparantly created 1.1.0 with the broken version.
The team's recommendedation was to re-create my packages with the current nuget.exe and re-deploy them to the NuGet servers. I did that and the result is version 1.1.1 of the Delay.Web.Helpers package and its associated Delay.Web.Helpers.SampleWebSite package. "Once bitten, twice shy", so I verified the install in both Visual Studio and Razor now that I know they're different and can fail independently.
Aside: There are no changes to the Delay.Web.Helpers assembly or samples in this release. The only changes are the necessary tweaks to the NuGet metadata for both packages to install successfully under Razor. Therefore, if you've already installed 1.1.0 successfully, there's no need to upgrade.
Further aside: The standalone ZIP file with the assembly, source code, automated tests, and sample web site is unaffected by this update.
To sum things up, if you created a NuGet package sometime around early April and you expect it to be installable with the Razor administration panel, I'd highly recommend trying it out to be sure!