Open files – An important warning: You must NOT have the file that you want to connect to open when you connect to the file for the first time. You must also not have it open when you try to refresh the data or refresh the preview in the PowerQuery Editor. The query won’t be harmed if you do have it open when trying to complete these actions; the Editor will just tell you that it’s not possible.
Using Excel files while the PowerQuery Editor is open – You might have noticed this already, but you can’t do any work in any Excel files if you have the PowerQuery Editor open. It’s a slightly irritating trait of PowerQuery, although it’s only true if you’re using PowerQuery in Excel, not PowerQuery in Power BI (we’ll get to that later).