Exception has been thrown by the target of an invocation. when enabling enterprise keywords

Question

I have the following code and I havent been able to find what the problem is. The exception is raised SOMETIMES in the last line of enable keywords, in the Update.

The thing is we create a site manually from code: then from code we also add a feature, and the problem is happening somewhere in the feature activated or some of its methods.

/// <param name="list"></param>
        public static void EnableEnterpriseKeywords(this SPList list)
        {
            Logger.LogDebug("SPListExtensions", "EnableEnterpriseKeywords(this SPList list)", "BEGIN");
            try
            {
                Assembly taxonomyAssembly = Assembly.LoadWithPartialName("Microsoft.SharePoint.Taxonomy");
                Type listFieldSettings = taxonomyAssembly.GetType("Microsoft.SharePoint.Taxonomy.MetadataListFieldSettings");
                object listSettings = listFieldSettings.GetConstructor(new Type[] { typeof(SPList) }).Invoke(new object[] { list });
                listFieldSettings.GetProperty("EnableKeywordsField", BindingFlags.NonPublic | BindingFlags.Instance).SetValue(listSettings, true, null);
                listFieldSettings.GetProperty("EnableMetadataPromotion", BindingFlags.NonPublic | BindingFlags.Instance).SetValue(listSettings, true, null);
                listFieldSettings.GetMethod("Update", BindingFlags.NonPublic | BindingFlags.Instance).Invoke(listSettings, null);
            }
            catch (Exception ex)
            {
                Logger.LogError("SPListExtensions", string.Format("EnableEnterpriseKeywords(this SPList list) - Error activating on list {0}", list.Title), ex);
                throw;
            }
            Logger.LogDebug("SPListExtensions", "EnableEnterpriseKeywords(this SPList list)", "END");
        }

Answer 1

Q: Did you have AllowUnsafeUpdates= True on the SpWeb?

I must say the way you use Reflection is interesting. Did you know that enabling Enterprise Keywords column is simple a matter of checking whether field exist and then adding it to the list as in:

 SPList list = SPContext.Current.Web.Lists.TryGetList("TargetList");
if (list != null)
                    {
                        SPField field = list.ParentWeb.AvailableFields["Enterprise Keywords"];
                        if (!list.Fields.ContainsField("Enterprise Keywords"))
                        {
                            list.Fields.Add(field);
                            list.Update();
                        }
                   }