[web] Added troubleshooting page for userguide.

web/config.toml

@@ -107,6 +107,10 @@ staticDir = ["dist", "static"]
   name = "Basics"
   identifier = "basics"
   weight = 1
+[[menu.userguide]]
+  name = "Troubleshooting"
+  identifier = "troubleshooting"
+  weight = 99
 
 # Tools sidebar top-level categories
 [[menu.tools]]

web/content/docs/userguide/troubleshooting/index.md

++++
+date = "2018-11-14T11:00:13+01`:00"
+title = "Troubleshooting"
+author = "Lars Bilke"
+weight = 99
+toc = true
+
+[menu]
+  [menu.userguide]
+    parent = "troubleshooting"
++++
+
+## Data Explorer
+
+### XSDError: Loaded schema file is invalid
+
+<i class="fas fa-exclamation-triangle"></i> Error message:
+
+```bash
+Error XSDError in http://www.opengeosys.org/images/xsd/OpenGeoSysCND.xsd, at line 1, column 1: Start tag expected.
+Error XSDError in file:///../bc/well.cnd, at line 5, column 195: Loaded schema file is invalid.
+XMLInterface::isValid() - XML File is invalid (in reference to schema ./OpenGeoSysCND.xsd).
+Error XSDError in http://www.opengeosys.org/images/xsd/OpenGeoSysCND.xsd, at line 1, column 1: Start tag expected.
+```
+
+This error may also apply to file conversion tools (e.g. `OGSFileConverter`).
+
+<i class="fas fa-arrow-right"></i> Solution:
+
+Open the affected file (e.g. `well.cnd` in this case) and remove the following parameter of the XML root element:
+
+```xml
+xsi:noNamespaceSchemaLocation="http://www.opengeosys.org/images/xsd/OpenGeoSysXXX.xsd"
+```
+
+where `XXX` can be `CND`, `GLI`, `PRJ` or `STN` depending on the file type.
+
+<details>
+    <summary>Background info:</summary>
+    The XSD files may be downloaded from a web location. We changed the protocol of our web site to `https://` but due to some weird behaviour of the Qt XML validation code it tries to download the file (even if it is available locally) and does not respect the URL redirection to `https://` of the web server. Simply removing the part solves the problem. The XML is still validated! Newer OGS versions do not write that parameter into files anymore, see https://github.com/ufz/ogs/pull/2198.
+</details>