Teradata BI Repository supports a limited form of MDX partial qualification. Member names must be fully qualified, but expressions like [Time].[Calendar].[Quarter].Members can be abbreviated to [Quarter].Members if Quarter is unique. Using fully-qualified name is the safest and most reliable method to express your calculation.
MDX expressions can be more complex. It is difficult to notice if there are unmatched pairs of brackets or many other syntax errors that could make an expression fail in Teradata OLAP Connector at runtime. Teradata Schema Workbench contains an MDX syntax checker (it is not a semantic checker) that catches many of these types of errors.
The syntax error message only indicates whether the syntax is valid or not. You must examine the MDX to find the error. See MDX Validation Errors.