How does the order of module compilation affect this error, especially with User-Defined Types?

While VBA's compiler is designed to handle dependencies, the "invalid forward reference" part of the error can sometimes arise from compilation order issues, particularly with User-Defined Types (UDTs) or complex inter-dependent Class Modules. 1. **User-Defined Types (UDTs):** If a UDT is defined in `Module1` and `Module2` attempts to use that UDT *before* `Module1` has been fully compiled and its definition is known, the error can occur. Ensure UDTs are declared `Public` in standard modules and consider placing them in a dedicated module. Always force a `Debug > Compile VBA Project` after UDT changes. 2. **Class Module Dependencies:** If `ClassA` uses a custom type defined in `ClassB`, and `ClassB` has not yet been compiled or its definition is unavailable, the compiler for `ClassA` will encounter an "uncompiled type." Structure your classes to minimize circular dependencies and ensure base classes can compile independently. `Debug > Compile VBA Project` is crucial here to force a re-evaluation of all modules.