What causes Expression.Error?

A column that the query references was renamed, removed, or reordered in the source. A function is called with an argument of the wrong type (e.g., passing text where a number is expected). An 'if' branch or try/otherwise expression returns incompatible types. A dynamic column reference (e.g., from Table.ColumnNames) returns a different column than expected. A custom function or parameter changed its expected input format

How do I fix Expression.Error?

Open the dataset in Power BI Desktop and refresh — the Query Editor will show exactly which step failed.. Click the failing step in Applied Steps to see the exact expression and the row that caused the error.. Check whether the source schema changed (columns added/removed/renamed) since the last successful refresh.. Use Table.HasColumns() or try...otherwise in your M query to handle schema changes gracefully.. If the error is a type mismatch, add an explicit type conversion: Text.From(), Number.From(), etc.. After fixing, publish the updated dataset to Power BI Service.

Medium severityquery

Power BI Refresh Error:
Expression.Error

What does this error mean?

A Power Query (M language) expression failed to evaluate during refresh. This error surfaces when query logic produces an unexpected value type, a missing column, or an unsupported operation.

Common causes

1A column that the query references was renamed, removed, or reordered in the source
2A function is called with an argument of the wrong type (e.g., passing text where a number is expected)
3An 'if' branch or try/otherwise expression returns incompatible types
4A dynamic column reference (e.g., from Table.ColumnNames) returns a different column than expected
5A custom function or parameter changed its expected input format

How to fix it

1Open the dataset in Power BI Desktop and refresh — the Query Editor will show exactly which step failed.
2Click the failing step in Applied Steps to see the exact expression and the row that caused the error.
3Check whether the source schema changed (columns added/removed/renamed) since the last successful refresh.
4Use Table.HasColumns() or try...otherwise in your M query to handle schema changes gracefully.
5If the error is a type mismatch, add an explicit type conversion: Text.From(), Number.From(), etc.
6After fixing, publish the updated dataset to Power BI Service.

Frequently asked questions

Does this error only affect the dataset or also the report?

The error occurs during the refresh — if the refresh fails, the report shows the last successfully loaded data, not an error. Users won't see a broken report, but the data will be stale.

How do I find which Power Query step is causing the error?

Open Power BI Desktop and attempt a refresh. Power Query highlights the failing step in the Query Editor. The error message typically includes the table name and step name.

Can query errors be caused by data changes in the source?

Yes — if the source returns a data type the query doesn't expect (e.g., a null value in a previously non-nullable column), the query evaluation fails.

Does this error affect all tables in the dataset?

Usually only the table whose query evaluation failed. Other queries in the dataset may succeed unless they depend on the failed query's output.

Source · learn.microsoft.com/en-us/power-bi/connect-data/service-dataflows-overview