Upgrade to March 2018 - Doesn't work

Good question, there's many successful upgrades, so there's something unique happening here. A few things to try:

1. If you are running both SSRS 2016 and PBIRS on the same machine, that can sometimes cause conflicts. Try to run on separate machines if possible. 

2. Check the URL reservations in the configuration tool, these can often be mis-configured to point the wrong server end points, or are not updated because windows is holding a lock on them and you need to reboot. 

3. Take a look at the report server log files, these will contain more detailed information about what's wrong and can help further diagnose the issue. 

4. Ensure you downloaded the latest copy of the March release, as you can see in the release notes, there are updates fixed in April and May.