I am loading in an existing xlsm (macro-enabled) file, filling it with data, and outputting the stream to be downloaded by the user. When I do, Excel says it “cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.”

I am loading in an existing xlsm (macro-enabled) file, filling it with data, and outputting the stream to be downloaded by the user. When I do, Excel says it “cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.”

I am loading in an existing xlsm (macro-enabled) file, filling it with data, and outputting the stream to be downloaded by the user. When I do, Excel says it “cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.”

I am loading in an existing xlsm (macro-enabled) file, filling it with data, and outputting the stream to be downloaded by the user. When I do, Excel says it “cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.”

I am loading in an existing xlsm (macro-enabled) file, filling it with data, and outputting the stream to be downloaded by the user. When I do, Excel says it “cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.”