Can't upload report to report server (Jan 2020 version)

Hi,

I'm having some issues uploading (any) reports from Power BI Desktop to Report Server. I get errors both when Saving As and when uploading from within Power BI itself.

The errors I'm receiving are, respectively:

• Upload via Report Server: "There was an error uploading your .pbix file. Verify that the file has not been corrupted and that the file extension matches the format of the file."
• Save As via PBI Desktop: "An error occurred while attempting to save the report to Power BI Report Server"

The versions I'm using are:

• Power BI Desktop (Optimised for Report Server): Version: 2.76.5678.1521 64-bit (January 2020)
• Power BI Report Server: Version 1.6.7364.4075 (January 2020)
• I have also tried the September 2019 version of Power BI Desktop and got the same issue.

To keep the test as simple as possible and (hopefully) eliminate any issues with the report itself I've created a simple "Hello World" report (one text box with "Hello World" in and that is literally it).

Any thoughts would be appreciated.