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