Solutions, features, and CompatibilityLevel

I recently came across an issue where certain feature definitions were not available in 2010 mode sites in one farm, but they were in another. It turned out that the parameters supplied to Install-SPSolution are the reason. Essentially, the difference was specifying -CompatibilityLevel {14,15} vs specifying nothing. I found this article to be very helpful: Planning Deployment of Farm Solutions for SharePoint 2013

Error codes

Just some notes to myself on some resources to help decipher error codes that I often come across. These are sometimes mentioned in the ULS logs with something like hresult= or hr=

• ErrCo.de - awesome and searchable set of error codes on pretty much everything
• Win32 Error Codes
• MS-ERREF
• Description of HRESULT

A potentially dangerous Request.Path value was detected from the client (%)

Recently came across an issue with an error like the following:
Application error when access {some-url}, Error=A potentially dangerous Request.Path value was detected from the client (%).
at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()
at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)

Looking more carefully at the URL, it turned out there was a %2520 in it. That is there was a space in the URL which was encoded into a %20, but then some errant code encoded it again into %2520.

What was tricky about this issue that I never saw my endpoint request actually get logged in ULS. Instead, it looked like this was caught by .NET.