1 files changed, 31 insertions, 1 deletions
diff --git a/doc/install/Troubleshooting.md b/doc/install/Troubleshooting.md
index 51699a39c..78ab5617d 100644
--- a/doc/install/Troubleshooting.md
+++ b/doc/install/Troubleshooting.md
@@ -12,7 +12,7 @@
   - If the System Administrator account becomes unavailable, a person leaving the organization for example, you can set a new system admin from the commandline using `./platform -assign_role -team_name="yourteam" -email="you@example.com" -role="system_admin"`. 
   - After assigning the role the user needs to log out and log back in before the System Administrator role is applied.
 
-#### Error Messages
+#### Mattermost Error Messages
 
 The following is a list of common error messages and solutions: 
 
@@ -29,8 +29,38 @@ The following is a list of common error messages and solutions:
  - This error can occur if you have manually manipulated the Mattermost database, typically with deletions. Mattermost is designed to serve as a searchable archive, and manual manipulation of the database elements compromises integrity and may prevent upgrade. 
  - **Solution:** Restore from database backup created prior to manual database updates, or reinstall the system.
 
+### Troubleshooting GitLab Mattermost
+
+- If you're having issues installing GitLab Mattermost with GitLab Omnibus, as a first step please turn on logging by updating the [log settings](https://github.com/mattermost/platform/blob/master/doc/install/Configuration-Settings.md#log-file-settings) section in your `config.json` file installed by omnibus, and they try a general web search for the error message you receive. 
+
+#### GitLab Mattermost Error Messages
+
+###### `We received an unexpected status code from the server (200)`
+
+- If you have upgraded from a pre-released version of GitLab Mattermost or if an unforseen issue has arrisen during the [upgrade procedure](https://github.com/mattermost/platform/blob/master/doc/install/Upgrade-Guide.md), you may be able to restore Mattermost using the following procedure: 
+  - `sudo stop mattermost`, so DB can be dropped 
+  - `sudo gitlab-ctl reconfigure`
+  - `sudo -u gitlab-psql /opt/gitlab/embedded/bin/dropdb -h /var/opt/gitlab/postgresql mattermost_production`
+  - `sudo start mattermost`
+  - `sudo gitlab-ctl reconfigure`
+  - [Manually set up GitLab SSO](https://github.com/mattermost/platform/blob/master/doc/integrations/Single-Sign-On/Gitlab.md) by copying Secret and ID into `/var/opt/gitlab/mattermost/config.json` 
+  - `sudo gitlab-ctl restart`
+
 ###### `Token request failed`
  - This error can appear in the web browser after attempting to create a new team with GitLab SSO enabled
  - **Solutions:** 
    1. Check that your SSL settings for the SSO provider match the `http://` or `https://` choice selected in `config.json` under `GitLabSettings`
    2. Follow steps 1 to 3 of the manual [GitLab SSO configuration procedure](https://github.com/mattermost/platform/blob/master/doc/integrations/Single-Sign-On/Gitlab.md) to confirm your `Secret` and `Id` settings in `config.json` match your GitLab settings, and if they don't, manually update `config.json` to the correct settings and see if this clears the issue. 
+
+###### `We couldn't find the existing account`
+  - This error appears when a user attempts to sign in using a single-sign-on option with an account that was not created using that single-sign-on option. For example, if a user creates Account A using email sign-up, then attempts to sign-in using GitLab SSO, the error appears since Account A was not created using GitLab SSO. 
+  - **Solution:** 
+    - If you're switching from email auth to GitLab SSO, and you're getting this issue on an admin account, consider deactivating your email-based account, then creating a new account with System Admin privileges using GitLab SSO. Specifically: 
+       1. Deactivate your email-based System Admin account (note: this process is [scheduled to improve](https://mattermost.atlassian.net/browse/PLT-975))
+         1. Temporarily turn off email verification (**System Console** > **Email Settings** > **Require Email Verification** > **false**, or set `"RequireEmailVerification": false` in `config.json`).
+         2. Change email for account to random address so you can create a new GitLab SSO account using your regular address.
+       2. Create a new Mattermost account using GitLab SSO
+         1. With GitLab SSO enabled, go to `https://domain.com/teamname` and sign-up for a new Mattermost account using your GitLab SSO account with preferred email address.
+         2. [Upgrade the new account to System Admin privileges](https://github.com/mattermost/platform/blob/master/doc/install/Troubleshooting.md#lost-system-administrator-account).
+       3. Deactivate the previous System Admin account that used email authentication.
+         1. Using the new GitLab SSO System Admin account go to **System Console** > **[TEAMNAME]** > **Users**, find the previous account and set it to "Inactive"