Intermission

Before moving on to the "/" and "\\" characters, let's also fix this error:

System.Web.HttpException
The resource cannot be found.
Details: Requested URL: /umbraco/~/umbraco/js/umbracoUpgradeChecker.js
Path error: should say - /umbraco/js/umbracoUpgradeChecker.js

Solution: in .../umbraco/presentation/umbraco/umbraco.aspx.cs line 104 change

sm.Scripts.Add(new ScriptReference(SystemDirectories.Umbraco + "/js/umbracoUpgradeChecker.js"));

to

string scriptPath = SystemDirectories.Umbraco + "/js/umbracoUpgradeChecker.js";
scriptPath = IOHelper.ResolveUrl(scriptPath);
ScriptReference scriptReference = new ScriptReference(scriptPath);

sm.Scripts.Add(scriptReference);