Query Error

[LegalAlien]

I recently inherited powerbi dashboard and I'm a complete novice. 

I joined two tables and started getting below error message: 

= let
tableWithOnlyPrimitiveTypes = Table.SelectColumns(Source, Table.ColumnsOfType(Source, {type nullable number, type nullable text, type nullable logical, type nullable date, type nullable datetime, type nullable datetimezone, type nullable time, type nullable duration})),
recordTypeFields = Type.RecordFields(Type.TableRow(Value.Type(tableWithOnlyPrimitiveTypes))),
fieldNames = Record.FieldNames(recordTypeFields),
fieldTypes = List.Transform(Record.ToList(recordTypeFields), each [Type]),
pairs = List.Transform(List.Positions(fieldNames), (i) => {fieldNames{i}, (v) => if v = null or Value.Is(v, fieldTypes{i}) then v else error [Message = "The type of the value does not match the type of the column.", Detail = v], fieldTypes{i}})
in
Table.TransformColumns(Source, pairs)"

Detected mismatch seems to be in the row1 with headers. All columns seem to show correct data type. the last steo for this erro is to add extra column with row numbers... there's nothing within my query and steps that adds this column. 

how can I resolve it?

[lbendlin]

I don't see where you are joining tables. The code you show is mainly dealing with meta data stuff.