I've just had such a problem setting this up and I wanted to post my solution here to see if anyone can confirm or deny what I think I'm seeing.
Here's my scenario. Designing a report using an Excel (xls) data source which I have copied to my local drive, so the path to the data source is c:\myfolder\myfile.xls. We have the enterprise On-Premises Data Gateway set up on a server which has access to the master copy of the xls file on a network drive. My user account has the relevant access to the gateway
I finish my report and publish to app.powerbi.com. Check the settings for the Dataset and get "Gateway not configured correctly" message. Click the button to 'Add to gateway' button and enter the various options, including changing the Full Path field so it is the correct path for the server to access the file (\\servername\fileshare\myfile.xls). Click OK/Save, at which point I am taken back to the Gateway settings on my data source. I can see at this point that it has not updated the file path to the file, it is still saying it is configured incorrectly and there is no dropdown to map the data source.
I tried various things to fix this, and eventually came across a solution. What I had to do was add an entry to my hosts file and create a new share on my local machine so that in the desktop app, I could set the data source as being \\servername\fileshare\myfile.xls matching what it would be on the server. If I publish the report now and use 'Add to Gateway', all I need to do is give it a data source name and set the credentials. Once I save the data source, I then get the option to Map the File path to the data source I just created.
My question is this: Is it really true that when creating reports in PowerBI desktop using a File as a data source, I need to use the exact same path to link to that data source as the Gateway would use? And if so, why does it give you the option to change the Full Path when creating your data source in the Service?
Can anyone point me to the documentation which specifies this? It would be useful to have this so I can explain it properly to the client I am working with on this!
