After looking through error.cpp, here are some to start with:

• {UNKNOWN_ERROR, "Unknown Error"},
• {ETOK_GENERAL, "Expected Token"},
• {ETOK_OPEN_PAREN, "Opening Parenthesis Expected"},
• {ETOK_CLOSE_PAREN, "Closing Parenthesis Expected"},
• {UTOK_GENERAL, "Unexpected Token"},
• {UTOK_LANG, "Wrong Language Error"},
• {UTOK_SUBORD, "Unexpected Subordination"},
• {MATH_GENERAL, "Math Error"},
• {MATH_DIV_DOMAIN, "Division Error"},
• {MATH_ROOT_DOMAIN, "Root Error"},
• {MATH_INVALID_OP, "Invalid Operator"},
• {MATH_NAN, "Invalid Operand"},
• {NDMATH_GENERAL, "Non-Decimal Math Error"},
• {NDMATH_DIGIT, "Illegal Digit"},
• {SYS_GENERAL, "System Error"},
• {SYS_MEM_ALLOC, "Memory Allocation Error"},
• {SYS_UNDERFLOW, "Underflow Error"},
• {SYS_OVERFLOW, "Overflow Error"},
• {SYS_NOT_FOUND, "Not Found"},
• {SYS_ACCESS, "System Access Error"},
• {SYS_SEG_FAULT, "Segmentation Fault"},
• {SYS_UNEX_TERM, "Unexpected Termination"},