The moc generates a single string literal that is stored into the 'stringdata' member of the 'qt_meta_stringdata_<namespace>_<class>_t' structure. If a class has a large number of enums constants, properties, then this string literal grows large enough that it hits the compiler limits.

For instance, with Microsoft Visual C++ 9.0 compiler, the limit is 65535 for a single string literal.