For the nth time, I missed this step in a new deployment, so blogging it down to remember for prosperity. Of course I will have to not forget to remember to this post.
Control Adapters are not loaded in a SharePoint site.
If the control adapter is part of a solution, ensure that the solution is deployed correctly (Get-SPSolution and the Deployed column is set to True)
Check the .browser file is uploaded correctly in all the WFE’s (App_Browsers directory)
Goto the WFE-1
for /d %d in (c:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\*) do @rmdir /s /q %d
for /d %d in (C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\*) do @rmdir /s /q %d
for /d %d in (C:\Windows\Microsoft.NET\Framework64\v2.0.50727\Temporary ASP.NET Files\*) do @rmdir /s /q %d
for /d %d in (C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\*) do @rmdir /s /q %d
Repeat the above steps in other WFE-s and also in CA server.
Now do an iisreset /start in all the servers.
Clear your browser cache and the control adapters should load fine.