I am getting the same issue across several of my dataflows now. If I run the sql query inside the dataflow it works but any reference to dataflows outside of that workspace has stopped working all of the sudden! I'm not sure how to even workaround this issue without undoing all my work. If this isn't a bug, can someone put me on the right path of what it might be please?
I'm also having this exact error. This error started to manifest itself on 05 April 2019 for me. This is occouring on multiple reports and can be created on demand.
I have attempted the following in trying to resolve;
Used the Merge Queries as Newoption rather than Merge Queries.
Have the dataflow table load into memory by checkingEnable Loadoption within Power Query Editor.
Rebuilt the Dataflows.
Rebuilt the report in the latest version of PBI Desktop (2.67.5404.981 64-bit (March 2019)).
Confirmed the gateway is on the latest version (3000.2.52 (march 2019 release 2)).
Removed the merge (obviously this works but is an unacceptable solution as I need that data merged).
Re-entered credentials for the dataflow in PBI Desktop and on the Service.
Error as taken from PBI Service;
Something went wrong
Unable to connect to the data source undefined.
Please try again later or contact support. If you contact support, please provide these details.
Underlying error code: -2147467259 Table: NonVoice.
Underlying error message: The columns parameter must be null, specify the number of columns, specify a list of column names, or specify a table type.
Cluster URI: WABI-US-EAST2-redirect.analysis.windows.net
Activity ID: 83703c77-276c-43e1-83ef-9790ea382b48
Request ID: ae46f037-b1dd-9558-316e-b59540007abf
Time: 2019-04-08 09:40:59Z