When attempting submission of tax returns, you are getting a message: 'The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel'
This is likely to happen if you are on older versions of Microsoft Windows and Internet Explorer or Microsoft Windows System that have not been updated.
There are a few possible solutions for this:
Run Windows Update on your computer, ensure that you have not rejected and hidden any Windows Updates.
Complete the update process for all Critical and Recommended updates. Specifically check and update
Windows Root Certificates on your system. This links to Microsoft website may help: https://support.microsoft.com/en-us/help/12373
For Windows XP computer, if it is not automatically updated, the root update package can be downloaded from Microsoft
Download Centre to update the list of root certificates on your computer to the list that is accepted by Microsoft
as part of the Microsoft Root Certificate Program. Root Update Package (intended for Windows XP only)
Update for Root Certificates [March 2011] (KB931125)
Import Government Gateway Certificate to your Windows Root Certificate store.