Medium severityquery
Power BI Refresh Error:
Microsoft.Data.Mashup.MashupValueException
What does this error mean?
The Power Query (Mashup) engine encountered a value that violates a constraint or is structurally incompatible with the expected output. This internal exception surfaces runtime evaluation failures in the M engine.
Common causes
- 1A column contains values outside the allowed range (e.g., dates before 1900 for legacy Date types)
- 2Binary data in a text column that cannot be serialized to the output format
- 3A null value in a column declared as non-nullable in the model
- 4A custom function returned an unexpected structured type (record, list, or table) where a scalar was expected
- 5A parameter or variable in the query contains a value that causes an evaluation loop or circular reference
How to fix it
- 1Isolate the problematic column by disabling columns one at a time and refreshing until the error disappears.
- 2Add explicit null handling and type guards in your Power Query transformations.
- 3Filter out known edge-case values (e.g., dates before 1900) using a conditional filter step.
- 4Replace complex custom functions with step-by-step transformations to narrow down which operation fails.
- 5Enable query folding where possible — server-side filtering handles edge cases before data reaches the M engine.