I have merged data from Excel to InDesign numerous times and have not encountered this problem before. I have a brand new document in InDesign and a clean, new data file from Excel saved as a CSV file. When I try to merge into InDesign, I get a message saying the data source cannot be opened.
Hi Ambernkrmc. You posted your question in the non-technical Lounge forum, which is where you can connect with your peers for conversations that don't directly relate to product help and support.
I’ll move your question to the InDesign forum so that you can get the answer you are looking for.
P.S. For a list of all available product forums, see https://forums.adobe.com/welcome/