diff --git a/AssemblyVersion.cs b/AssemblyVersion.cs
index be2b2df..1a731a3 100644
--- a/AssemblyVersion.cs
+++ b/AssemblyVersion.cs
@@ -16,5 +16,5 @@ using System.Reflection;
 //
 // You can specify all the values or you can default the Revision and Build Numbers 
 // by using the '*' as shown below:
-[assembly: AssemblyVersion("3.0.3.555")]
-[assembly: AssemblyFileVersion("3.0.3.555")]
+[assembly: AssemblyVersion("3.0.3.556")]
+[assembly: AssemblyFileVersion("3.0.3.556")]
diff --git a/Core/UrlTools.cs b/Core/UrlTools.cs
index 97e5341..e370076 100644
--- a/Core/UrlTools.cs
+++ b/Core/UrlTools.cs
@@ -132,9 +132,15 @@ namespace ScrewTurn.Wiki {
 
 			if(tempString.StartsWith("++")) return tempString.Substring(2);
 
-			string nspace = HttpContext.Current.Request["NS"];
-			if(string.IsNullOrEmpty(nspace)) nspace = null;
-			if(nspace == null) nspace = GetCurrentNamespace();
+			string nspace = null;
+			if(HttpContext.Current != null) {
+				// HttpContext.Current can be null when executing asynchronous tasks
+				// The point is that BuildUrl is called without namespace info only from the web application, so HttpContext is available in that case
+				// When the context is not available, in all cases BuildUrl is called by the formatter, that has already included namespace info in the URL
+				nspace = HttpContext.Current.Request["NS"];
+				if(string.IsNullOrEmpty(nspace)) nspace = null;
+				if(nspace == null) nspace = GetCurrentNamespace();
+			}
 			if(string.IsNullOrEmpty(nspace)) nspace = null;
 			else nspace = Pages.FindNamespace(nspace).Name;