Are there specific syntax differences between PHP4 and PHP5 that can lead to script errors?

Yes, there are specific syntax differences between PHP4 and PHP5 that can lead to script errors. One common issue is the use of the "new" keyword for object instantiation. In PHP4, the "new" keyword was optional, while in PHP5, it is required. To fix this issue, make sure to always use the "new" keyword when creating new objects in PHP5.

// PHP4 code
$object = MyClass($arg1, $arg2);

// PHP5 code
$object = new MyClass($arg1, $arg2);