Symptoms
On attempt to access the Office 365 tab in CCP the following error appears:
"Unknown error occurred"
The following error could also be seen in the browser console:
[HttpCompileException]: c:\inetpub\wwwroot\O365Sigmax\App_Code\Import\ImportHelper.cs(902): error CS0163: Control cannot fall through from one case label ('case 4:) to another
at System.Web.Compilation.AssemblyBuilder.Compile()
at System.Web.Compilation.BuildProvidersCompiler.PerformBuild()
Cause
Someone replaced the ImportHelper.cs source code file in the Endpoint directory.
Resolution
Replace the ImportHelper.cs source code file with the original one and recycle the Application Pool.