Unable to edit or delete data driven subscription - rsInternal Error

I have a data driven subscription that I am trying to edit or delete. If I do either, I get a message

An internal error occurred on the report server. See the error log for more details. (rsInternalError) Get Online Help The status is pending. Help! Thank you

I found in a SQL Dmpr0009.log file the following error: library!ReportServer_0-2!2410!02/27/2015-09:21:38:: 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.;