T1C-JS Guide (v2)


Microsoft Edge not allowing connections to localhost

In some cases we have observed Microsoft Edge blocking connections to localhost, making it unable to communicate with the installed GCL instance.
Microsoft runs as a modern Windows app, which means it has network isolation enabled by default for security reasons. However, by default an exception is made for loopback/localhost addresses. This means that on most Edge browsers, communication with the GCL instance will not be a problem.
In specific cases though (exact reasons as yet unknown), it seems that this exception is ignored or not applied correctly, blocking communication with localhost.
If you find yourself in this situation, try the following options to resolve:

A. Enable the loopback option

Open your browser and type about:flags in the address bar. This will open a hidden browser settings menu. Locate the Developer settings and make sure the option to Allow localhost loopback is checked.
The number of options under the Developer settings heading can vary between the different versions of Microsoft Edge, but the localhost loopback option should always be there.
Once the option is enabled, fully close down Microsoft Edge and restart the browser.
If this option was already enabled, try disabling it, restarting the browser and then re-enabling.
Check if this has resolved the issue. If not, proceed to option B.
B. Use the command prompt
Open a command prompt as administrator(!) and execute the following command:
CheckNetIsolation LoopbackExempt -a -n=Microsoft.MicrosoftEdge_8wekyb3d8bbwe
Windows will respond with the message OK.
Restart Microsoft Edge and check if the issue is resolved.

Additional info can be found here:

I keep getting generic Network Errors (code 999)

When something goes wrong during transmission of a request, the library will return a generic Network Error with code 999.
If you systematically keep getting these errors, this usually indicates one of the following:
  • No network connection is available
  • An SSL connection could not be established
To fix, first make sure you are connected to the Internet and you can reach some well-known website (i.e. google.com or similar).
If internet connectivity is OK, make sure that the browser you are using supports TLS 1.2. This is especially relevant for users of Internet Explorer 10: by default only TLS 1.0 is enabled in this browser. If you or one of your users are still on Internet Explorer 10, see the steps below to enable TLS 1.2.

Enabling TLS 1.2 in Internet Explorer 10

Open the settings menu and click on Internet options:
Navigate to the Advanced tab:
Scroll down to Security Options:
Locate the option Use TLS 1.2 and make sure it is checked:
Click OK to save the settings.

The Trust1Connector certificate has expired

The Trust1Connector is designed to automatically renew its certificate if expired, or re-create it if missing. Should the process of renewing an existing certificate fail however, the following steps can be undertaken to remedy it:


  1. 1.
    Open the Windows Certificate Manager (certmgr.exe)
  2. 2.
    Locate the expired Trust1Connector certificate by right-clicking on the top-level item Certificates - Local Computer and searching for localhost or trust1connector (depending on the installed version):
  3. 3.
    If the search yields multiple results, select the certificate past its expiration date:
  4. 4.
    Right-click the expire certificate, select Delete and confirm the deletion action:
  5. 5.
    Once the certificate is deleted, restart your computer. At the next startup, a new certificate will have been generated.

Mac OS

  1. 1.
    Open the Mac OS Keychain Access by pressing ⌘ + space and typing its name:
  2. 2.
    Look under Certificates and select the expired certificate with the name localhost or trust1connector (depending on the installed version):
  3. 3.
    Right-click the certificate and select the Delete action, enter your password when prompted:
  4. 4.
    Restart your device.


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