If you come across this problem then the notes and a workaround (move the FckHTML DLL from bin/providers to bin) are here:
Just posting this as it took me a while to find it.
Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.
Parser Error Message: Could not load type 'DotNetNuke.HtmlEditor.FckHtmlEditorProvider.fcklinkgallery'.