When upgrading to 8.7.1, the Install Readiness Check may prevent you from continuing with the upgrade due to Microsoft Report Viewer not being installed. You may already have Microsoft Report Viewer installed, however, this check still comes up as seen here:
With the release of 8.7.1, Microsoft Report Viewer 2015 is required, whereas it was 2008. In addition, there is a prerequisite to install Microsoft SQL Server System CLR Type before installing Microsoft Report Viewer 2015 Runtime.
Upgrading to ITMS 8.7.1
Prerequisites were not installed.
Please click on the About Microsoft Report Viewer link in the install readiness check. This will then take you to another webpage with links to download the needed prerequisites as seen here:
Other Notes:
.NET 4.8 is also a new requirement for installing the SMP and Site Servers too.
If a Reboot is needed, you will not be able to pass the Install Readiness Check so consider doing a reboot before start the upgrade. And always login as the App ID when doing an upgrade.