Certificate Chain Not Trusted Error Effecting PowerBI Only

This worked for me too.

For those who want more detailed instructions:

1. Open your Power BI Desktop app
2. Click 'File'
3. Click 'Options and Settings'
4. Click 'Data Source settings'
5. Select the offending SQL server instance, from the list of data sources
6. Click 'Edit permissions' button at base of prompt screen
7. In this new prompt screen, under the 'Credentials' section, click the 'Edit' button to open a new prompt and select 'Windows'
8. Select either 'Use my current credentials' or 'Use alternate crednetials' (up to you, I just used mine)
9. Click' Save' button to close this prompt and return to the 'Edit Permissions' prompt screen.
   • In here there is an 'Encrypt connections' option. If your server accepts encrypted connections this will need to be ticked, mine doesn't and so I left it blank.
   • If you're not sure, don't worry. When you click 'Refresh All' a prompt will tell you if you need to be unencrypted and you can come back and untick this box.

Does anyone know why this works?
In my organisation, my windows account is used as my MS account, so it is the same thing, so why does the MS option not work. It used to work, and has done for over a year, and what is more the Power BI cloud service data model continued refreshing, using the MS account, fine, whilst the desktop one refused too. Spoke with head of IT and he is is equally flummoxed, saying that becuase we use our windows accounts as our orgnisational MS ones, they're the same thing and so there should be no issue...feels like a Power BI glitch to me!