sp_send_dbmail fails with attachment

Too long to comment.

Change @exclude_query_output = 0 to @exclude_query_output = 1. This will likely print a message (error message) on what is going on.

In your example, I was able to get around the error:

Failed to initialize sqlcmd library with error number -2147024809.

that I got and I expect you'll likely get by changing @query_result_header = 0 to @query_result_header = 1. I'm not sure why the lack of headers is causing it to fail, but it fixed it on my dev box.