Issue

If you’re trying to debug a mapped custom page in SharePoint from PowerShell, but come across this issue:

PS C:> $webapp = get-spwebapplication http://sp2010
$webapp.GetMappedPage([Microsoft.SharePoint.Administration.SPWebApplication.SPCustomPage]::Error)
Unable to find type [Microsoft.SharePoint.Administration.SPWebApplication.SPCustomPage]: make sure that the 
assembly containing this type is loaded.
At line:2 char:90
+ $webapp.GetMappedPage([Microsoft.SharePoint.Administration.SPWebApplication.SPCustomPage] <<<< ::Error)
    + CategoryInfo          : InvalidOperation: (Microsoft.Share...on.SPCustomPage:String) [], RuntimeException
    + FullyQualifiedErrorId : TypeNotFound

Solution

Try this instead:

$webapp.GetMappedPage([Microsoft.SharePoint.Administration.SPWebApplication+SPCustomPage]::Signout)

The Clue

I’m not sure why the syntax is different for this. I would have expected a period instead of a plus there before SPCustomPage. None of my research on Enums showed a plus sign, but finally I noticed this:

PS C:> $webapp.GetMappedPage

MemberType          : Method
OverloadDefinitions : {string GetMappedPage(Microsoft.SharePoint.Administration.SPWebApplication+SPCustomPage key), 
	string GetMappedPage(string page)}
TypeNameOfValue     : System.Management.Automation.PSMethod
Value               : string GetMappedPage(Microsoft.SharePoint.Administration.SPWebApplication+SPCustomPage key), 
	string GetMappedPage(string page)
Name                : GetMappedPage
IsInstance          : True

Reference

Mapping Custom Error Pages for SharePoint 2010 Site, Ram Prasad MCTS, http://www.spdeveloper.co.in/articles/pages/custom-error-pages-for-sharepoint2010-sites.aspx