Postfix Expression Evaluation

You are tasked with evaluating a postfix expression using a stack. The expression consists of non-negative integers and the following operators: '+', '-', '*', '/'. You should assume the operands and operators are separated by spaces. The result of the evaluation should be an integer. If an invalid expression is encountered, return 'Error'. Input Format: - A single string representing the postfix expression. Output Format: - A single integer result or 'Error'. Example: Input: 5 3 + 2 * 4 - Output: 10