Error Messages Reference

Common error messages from Studio Pro, mxcli, and the MDL parser, with explanations and solutions.

Studio Pro Errors

These errors appear when opening a project in Studio Pro after modification by mxcli.

TypeCacheUnknownTypeException

TypeCacheUnknownTypeException: The type cache does not contain a type
with qualified name DomainModels$Index

Cause: The BSON $Type field uses the qualifiedName instead of the storageName. These are often identical, but not always.

Solution: Check the metamodel reflection data for the correct storage name:

Look up the type in reference/mendixmodellib/reflection-data/<version>-structures.json and use the storageName field value.

CE0463: Widget definition changed

CE0463: The widget definition of 'DataGrid2' has changed.

Cause: The widget’s WidgetObject properties do not match its PropertyTypes schema. This happens when:

• A widget template is missing properties
• Property values have incorrect types
• The template was extracted from a different Mendix version

Solution:

1. Create the same widget manually in Studio Pro
2. Extract its BSON from the saved project
3. Compare the template’s object section against the Studio Pro version
4. Update sdk/widgets/templates/<version>/<Widget>.json to match

See the debug workflow in .claude/skills/debug-bson.md for step-by-step instructions.

CE0066: Entity access is out of date

CE0066: Entity access for 'MyModule.Customer' is out of date.

Cause: Association MemberAccess entries were added to the wrong entity. In Mendix, association access rules must only be on the FROM entity (the one stored in ParentPointer), not the TO entity.

Solution: Ensure MemberAccess entries for associations are added only to the entity that owns the foreign key (the FROM side of the association). Remove any association MemberAccess entries from the TO entity.

System.ArgumentNullException (ValidationRule)

System.ArgumentNullException: Value cannot be null.

Cause: A validation rule’s Attribute field uses a binary UUID instead of a qualified name string. The metamodel specifies BY_NAME_REFERENCE for this field.

Solution: Use a qualified name string (e.g., "Module.Entity.Attribute") for the Attribute field in ValidationRule BSON, not a binary UUID.

mxcli Parser Errors

Mismatched input

Line 3, Col 42: mismatched input ')' expecting ','

Cause: Syntax error in the MDL statement – typically a missing comma, semicolon, or unmatched bracket.

Solution: Check the MDL syntax at the reported line and column. Common issues:

• Missing commas between attribute definitions
• Missing semicolons at the end of statements
• Unmatched parentheses or curly braces

No viable alternative

Line 1, Col 0: no viable alternative at input 'CREAT'

Cause: Unrecognized keyword or misspelling.

Solution: Check the keyword spelling. MDL keywords are case-insensitive but must be valid. Run mxcli syntax keywords for the full keyword list.

mxcli Execution Errors

Module not found

Error: module 'MyModule' not found in project

Cause: The referenced module does not exist in the .mpr file.

Solution: Check the module name with SHOW MODULES and verify the spelling. Module names are case-sensitive.

Entity not found

Error: entity 'MyModule.Customer' not found

Cause: The referenced entity does not exist in the specified module.

Solution: Check with SHOW ENTITIES IN MyModule. If the entity was just created, ensure the create statement executed successfully before referencing it.

Reference validation failed

Error: unresolved reference 'MyModule.NonExistent' at line 5

Cause: A qualified name references an element that does not exist in the project. This error appears with mxcli check script.mdl -p app.mpr --references.

Solution: Verify the referenced element exists, or create it before the referencing statement.

BSON Serialization Errors

Wrong array prefix

Symptom: Studio Pro fails to load the project or shows garbled data.

Cause: Missing or incorrect integer prefix in BSON arrays. Mendix BSON arrays require a count/type prefix as the first element:

{
  "Attributes": [3, { ... }, { ... }]
}

Solution: Ensure all arrays include the correct prefix value (typically 2 or 3). Check existing BSON output for the correct prefix for each array property.

Wrong reference format

Symptom: Studio Pro crashes or shows null reference errors.

Cause: Using BY_ID_REFERENCE (binary UUID) where BY_NAME_REFERENCE (qualified string) is expected, or vice versa.

Solution: Check the metamodel reflection data for the property’s kind field:

• BY_ID_REFERENCE -> use binary UUID
• BY_NAME_REFERENCE -> use qualified name string (e.g., "Module.Entity.Attribute")