diff --git a/Server-Diagnostics---Troubleshooting.md b/Server-Diagnostics---Troubleshooting.md
index b9ef286..ff6740e 100644
--- a/Server-Diagnostics---Troubleshooting.md
+++ b/Server-Diagnostics---Troubleshooting.md
@@ -12,6 +12,19 @@ Since 3.0.0 a special command option exists to verify the storage of the collect
 
 It should not report any errors, otherwise particular VCF or ICS files have to be fixed manually.
 
+## Storage verification reports: "Invalid item"
+
+Upload reported file to https://icalendar.org/validator.html and run validation.
+
+* Result: external validator reports also an error -> fix manually or delete file
+* Result: external validator reports OK -> continue here: https://github.com/Kozea/Radicale/wiki/Reporting-Issues
+
+## Storage verification reports: "Invalid collection '$NAME': '$TYPE' must not have child collections
+
+Background: "radicale" do not support a nested storage hierachy.
+
+Solution: check for any folder in <NAME> which itself is a collection and move it on same level as $NAME. Check also content of related ".Radicale.props" file
+
 # Listen Status
 
 ## Radicale started, it's listen on configured IP/ports