diff --git a/Engine/ScriptAnalyzer.cs b/Engine/ScriptAnalyzer.cs
index 1e7227b47..07b891ae3 100644
--- a/Engine/ScriptAnalyzer.cs
+++ b/Engine/ScriptAnalyzer.cs
@@ -764,8 +764,8 @@ private List<ExternalRule> GetExternalRule(string[] moduleNames)
                             {
                                 dynamic description = helpContent[0].Properties["Description"];
 
-                                if (null != description)
-                                {
+                                if (null != description && null != description.Value && description.Value.GetType().IsArray)
+                                {                                    
                                     desc = description.Value[0].Text;
                                 }
                             }
diff --git a/appveyor.yml b/appveyor.yml
index 50865ac4c..6c3e376d6 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,5 +1,5 @@
-# WS2012R2 image with April WMF5.0
-os: unstable
+# Image with WMF5.0 RTM
+os: "WMF 5"
 
 # clone directory
 clone_folder: c:\projects\psscriptanalyzer