New Post: Loading SSRS Excel spreadsheet throws Object reference not set error

Same here using EXCELOPENXML.

It looks like SSRS is putting invalid characts into the XML. It may be related to this EPPlus thread: https://epplus.codeplex.com/workitem/14948

Haven't found a way around yet.

Remember: EXCELOPENXML produces a openXML documents instead of EXCELs old binary format. XLS != XLSX