Background: We have Power BI Report Server running for the past 1 year with users accessing reports perfectly and doing great things with Business. The reports that are built usually using "Import" methodology and had daily refreshes in the morning. Reports access the data from Excel, SQL Server & SQL Server Analysis Services.
Problem: Users complain about reports are not opening and giving error "Unable to load Data Model". When we connect to the machine we checked Memory & CPU both were fine & we thought that there might be a Service issue so we restarted the service but receive the following error then we tried to change the service user to admin any applied changes in the Report Server configuration still we received the following error
System.InvalidOperationException: Cannot start service PowerBIReportServer on computer 'Server'. ---> System.ComponentModel.Win32Exception: The service did not respond to the start or control request in a timely fashion
--- End of inner exception stack trace ---
at System.ServiceProcess.ServiceController.Start(String args)
at ReportServicesConfigUI.Panels.ConfigurationPanelWithErrors.StartOrStopServiceTask(Boolean start, String serviceName)
Analysis: Upon checking we realized that we had "Zero" space in our Power BI Report Server DB Drive (same drive had Power BI Report Server Installation); we thought that this is the real reason for Power BI Report Server Service issue; we cleared the space by shrinking logs of DB. Then we tried to start the service again, the issue persists having the same error with space is available now.
Root Cause: With reading logs under the report server log folder and tracing we figured out that "web.config" & "rssrvpolicy.config" files are of "Zero" bytes (i.e. nothing in those files), amazing thing was that we had done nothing to them but still they are empty.
The reason they were empty because as soon as you apply changes by using "Report Server Configuration Manager" it recreates "web.config" & "rssrvpolicy.config" files since we had zero space in the drive those files were replaced by Empty files.
Solution: Fortunately, we had backup of those files, we restored that and started the service and it worked perfectly.
Lesson Learned. - Data Model error caused by the Analysis Services service run thru Power BI Report Server. There is no service in Services for that. This is part of the Power BI Report Server Service. - Always check space in drives when receiving an error of unhandled exceptions. - Do not make any changes in Power BI Report Server configuration unless you had space in the drive. - Always create a backup of existing config files. - Create a trigger email for space issues.
I hope this might help some of the users as we created a mess out of such a simple issue.