This article provides information about the error message:
Cannot execute as the database principal because the principal ewreportuser does not exist, this type of principal cannot be impersonated, or you do not have permission.
All current versions of Patch Manager
You are unable to run Patch Manager reports because the ewreportuser user does not exist on the SQL server you are reporting against.
Use the dbhelper application to recreate the user on the affected SQL server:
USE EminentWare
GO
EXEC sp_dropuser 'ewreportuser'
GO
dbhelper /s sqlServer /p createlogins /u serviceAcct /o c:\output.ini
If the above does not resolve your issue please delete and recreate the user in SQL Server Management Studio (SSMS) for the server logins and the Eminentware logins.