Updated max sessions description to indicate that you need to restart Tomcat for it to take effect.

src/main/java/org/nrg/xnat/services/XnatAppInfo.java

@@ -147,6 +147,9 @@ public class XnatAppInfo {
                         catch(InvalidPreferenceName e){
                             _log.error("",e);
                         }
+                        catch(NullPointerException e){
+                            _log.error("Error getting site config preferences.",e);
+                        }
                     }
                 }
             }

src/main/resources/META-INF/xnat/preferences/site-config.properties

@@ -23,7 +23,7 @@ UI.show-left-bar-search=true
 UI.show-left-bar-browse=true
 UI.show-manage-files=true
 UI.allow-non-admin-project-creation=true
-UI.login_failure_message=Your login attempt failed because the username and password combination you provided was invalid. After %d failed login attempts, your user account will be locked. If you believe your account is currently locked, you can:<ul><li>Unlock it by resetting your password</li><li>Wait one hour for it to unlock automatically</li></ul>
+UI.login_failure_message=Your login attempt failed because the username and password combination you provided was invalid or the site is currently at the maximum number of user sessions. After %d failed login attempts, your user account will be locked. If you believe your account is currently locked, you can:<ul><li>Unlock it by resetting your password</li><li>Wait one hour for it to unlock automatically</li></ul>
 
 # Indicates whether access to the list of system users should be restricted to site administrators only.
 restrictUserListAccessToAdmins=false

src/main/resources/META-INF/xnat/spawner/site-admin-elements.yaml

@@ -320,7 +320,7 @@ userLoginsSessionControls:
             kind: panel.input.number
             name: ":sessions.concurrent_max"
             label: Maximum Concurrent Sessions
-            description: The maximum number of permitted sessions a user can have open simultaneously
+            description: The maximum number of permitted sessions a user can have open simultaneously. You must restart Tomcat for changes to this to take effect.
         loginFailureMessage:
             kind: panel.textarea
             name: ":UI.login_failure_message"