Formula.Firewall: (step 'Invoked Custom Function') references other queries

Hi Baskar,

Based on my test, I can reproduce a similar error as yours. Clearly we cannot combine an external data source with another query. Please check the blog to solve your issue.

At first, I create a parameter that contains file path/name and let the source is equal to the parameter. Then the M code is like this.

let
    Source = Folder.Files(Parameter1),
    #"Invoke Custom Function1" = Table.AddColumn(Source, "Transform File from C (2)", each #"Transform File from C (2)"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File from C (2)"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File from C (2)", Table.ColumnNames(#"Transform File from C (2)"(#"Sample File (2)"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"ID", Int64.Type}, {"name", type text}}),
    #"Merged Queries" = Table.NestedJoin(#"Changed Type",{"name"},#"Transform Sample File from C",{"name"},"Transform Sample File from C",JoinKind.LeftOuter)
in
#"Merged Queries"

And based on the above blog, I take the steps and change the M code as below.

let
    Source = testlist,
    #"Invoke Custom Function1" = Table.AddColumn(Source, "Transform File from C (2)", each #"Transform File from C (2)"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File from C (2)"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File from C (2)", Table.ColumnNames(#"Transform File from C (2)"(#"Sample File (2)"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"ID", Int64.Type}, {"name", type text}}),
    #"Merged Queries" = Table.NestedJoin(#"Changed Type",{"name"},#"Transform Sample File from C",{"name"},"Transform Sample File from C",JoinKind.LeftOuter)
in
#"Merged Queries"

Then we can get the result without no issue. If you still get errors, please share your Power Query code here.

Regards,

Frank