DataFormat.Error: We couldn't Convert to Number - But it's all Text and I haven't changed type

Please post the code from the Advanced Editor and tell us what the column is that gives the error.

There are some steps and the use case requires merged queries. The initial import Transform File:

let
    Source = Csv.Document(Parameter2,[Delimiter=";", Columns=33, Encoding=1252, QuoteStyle=QuoteStyle.None]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type datetime}, {"SAMPLE COLUMN", type datetime}, {"ERROR GENERATING COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}, {"SAMPLE COLUMN", type text}})
in
    #"Changed Type"

Then the Query on the same data:

let
    Source = SharePoint.Files("https://Source.sharepoint.com/teams/GO365_SourceSite", [ApiVersion = 15]),
    #"Filtered Rows" = Table.SelectRows(Source, each Text.Contains([Folder Path], "Filter Value") and not Text.Contains([Folder Path], "Filter Value")),
    #"Filtered Hidden Files1" = Table.SelectRows(#"Filtered Rows", each [Attributes]?[Hidden]? <> true),
    #"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File (2)", each #"Transform File (2)"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File (2)"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File (2)", Table.ColumnNames(#"Transform File (2)"(#"Sample File (2)"))),
    #"Duplicated Column" = Table.DuplicateColumn(#"Expanded Table Column1", "SAMPLE COLUMN", "SAMPLE COLUMN - Copy"),
    #"Duplicated Column1" = Table.DuplicateColumn(#"Duplicated Column", "SAMPLE COLUMN1", "SAMPLE COLUMN1 - Copy"),
    #"Merged Columns" = Table.CombineColumns(#"Duplicated Column1",{"SAMPLE COLUMN - Copy", "SAMPLE COLUMN1 - Copy"},Combiner.CombineTextByDelimiter(" ", QuoteStyle.None),"ID"),
    #"Changed Type" = Table.TransformColumnTypes(#"Merged Columns",{{"ERROR GENERATING COLUMN", type text}})
in
    #"Changed Type"

Then the output query (The error occurs at #"Filtered Rows" step):

let
    Source = Table.NestedJoin(#"Client List", {"IDENTIFIERA"}, #"Status", {"IDENTIFIERB"}, "Status", JoinKind.LeftOuter),
    #"Expanded Status" = Table.ExpandTableColumn(Source, "Status", {"Code", "SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN"}, {"Status.Code", "Status.SAMPLE COLUMN", "Status.SAMPLE COLUMN", "Status.SAMPLE COLUMN", "Status.SAMPLE COLUMN"}),
    #"Duplicated Column" = Table.DuplicateColumn(#"Expanded Status", "Account", "Account - Copy"),
    #"Duplicated Column1" = Table.DuplicateColumn(#"Duplicated Column", "Status.SAMPLE COLUMN", "Status.SAMPLE COLUMN - Copy"),
    #"Merged Columns" = Table.CombineColumns(#"Duplicated Column1",{"Account - Copy", "Status.SAMPLE COLUMN - Copy"},Combiner.CombineTextByDelimiter(" ", QuoteStyle.None),"ID"),
    #"Merged Queries" = Table.NestedJoin(#"Merged Columns", {"Status.SAMPLE COLUMN"}, #"QUERY HFA", {"SAMPLE COLUMN"}, "SAMPLE COLUMN HFA", JoinKind.LeftOuter),
    #"Expanded HFA" = Table.ExpandTableColumn(#"Merged Queries", "SAMPLE COLUMN HFA", {"SAMPLE COLUMN", "SAMPLE COLUMN TYPE"}, {"HFA.SAMPLE COLUMN", "HFA.SAMPLE COLUMN"}),
    #"Merged Queries1" = Table.NestedJoin(#"Expanded HFA", {"HFA.SAMPLE COLUMN"}, #"ERROR QUERY", {"SAMPLE COLUMN"}, "ERROR QUERY", JoinKind.LeftOuter),
    #"Expanded ERROR QUERY" = Table.ExpandTableColumn(#"Merged Queries1", "ERROR QUERY", {"SAMPLE COLUMN", "ERROR GENERATING COLUMN"}, {"ERROR QUERY.SAMPLE COLUMN", "ERROR QUERY.ERROR GENERATING COLUMN"}),
    #"Added Conditional Column" = Table.AddColumn(#"Expanded ERROR QUERY", "Match Check", each if [ERROR QUERY.ERROR GENERATING COLUMN] = null then "No" else if [ERROR QUERY.ERROR GENERATING COLUMN] = "" then "No" else if [Account] = [ERROR QUERY.ERROR GENERATING COLUMN] then "Yes" else "No"),
    #"Filtered Rows" = Table.SelectRows(#"Added Conditional Column", each ([Match] = "Yes")),
    #"Merged Queries2" = Table.NestedJoin(#"Filtered Rows", {"Status.Code"}, OTHER QUERY, {"Code"}, "OTHER QUERY", JoinKind.LeftOuter),
    #"Expanded OTHER QUERY" = Table.ExpandTableColumn(#"Merged Queries2", "OTHER QUERY", {"SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN", "SAMPLE COLUMN"}, {"OTHER QUERY.SAMPLE COLUMN", "OTHER QUERY.SAMPLE COLUMN", "OTHER QUERY.SAMPLE COLUMN", "OTHER QUERY.SAMPLE COLUMN", "OTHER QUERY.SAMPLE COLUMN", "OTHER QUERY.SAMPLE COLUMN", "OTHER QUERY.SAMPLE COLUMN"}),
    #"Added Conditional Column1" = Table.AddColumn(#"Expanded OTHER QUERY", "Direction Match", each if [Direction] = [#"OTHER QUERY.SAMPLE COLUMN"] then "Yes" else null),
    #"Filtered Rows1" = Table.SelectRows(#"Added Conditional Column1", each [Direction Match] <> null and [Direction Match] <> "")
in
    #"Filtered Rows1"

I've named the column as ERROR GENERATING COLUMN throughout. The error occurs when the related conditional column is filtered. I cannot see why Power Query is trying to convert this data from the error column to a number at this point?