SSRS - Cannot edit data driven subscription / delete report

Issue

Recently when trying to edit an existing data driven subscription I received an error message through the web front end which didn’t prove very useful. 

 

This all happened shortly after I encountered the server responding slowly, in hindsight I think I may have pressed finish twice when editing the subscription and created two copies of it.

Steps I took to investigate

These are the steps I took to investigate, it might prove useful for looking for similar problems yourself.

I looked at the internal logs on the reporting services server (which in SSRS 2014 were located in C:\Program Files\Microsoft SQL Server\MSRS12.MSSQLSERVER\Reporting Services\LogFiles), inside I eventually found;

library!ReportServer_0-9!1514!11/20/2018-13:05:00:: i INFO: Call to GetSystemPropertiesAction().

library!ReportServer_0-9!1514!11/20/2018-13:05:00:: i INFO: Call to GetItemTypeAction(/email_reports/HR - Leaver Email).

library!ReportServer_0-9!1514!11/20/2018-13:05:00:: i INFO: Call to GetReportParametersAction(/email_reports/HR - Leaver Email).

library!ReportServer_0-9!1268!11/20/2018-13:05:00:: i INFO: Call to GetSubscriptionPropertiessAction(ed4ccbeb-2907-45db-b911-84d16c547e0c).

library!ReportServer_0-9!1268!11/20/2018-13:05:00:: e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.InternalCatalogException: Adding more than one data source with null original name, Microsoft.ReportingServices.Diagnostics.Utilities.InternalCatalogException: An internal error occurred on the report server. See the error log for more details.;

Looking at the entry in the log file I can see the report folder/report name in yellow which leads me to believe I am in the right place in the log file (corresponding with the date/time of the error) and the error description in red leads me to believe the issue is relating to the data source. 

I decided that the easiest course of action was to delete the subscription and recreate it, I went into SSMS on the reports server and found the table “[ReportServer].[dbo].[Subscriptions]” this gave me sufficient from the “datasettings” column to recreate the subscription.