The BDP error (BadSubscript) typically occurs in programming languages when an invalid subscript or index is used to access an array, list, or similar data structure. This error happens when an attempt is made to reference an element at an index that doesn’t exist or is out of range. Common causes include using negative indices, exceeding the array’s bounds, or passing non-integer values as subscripts. To resolve this error, verify the array’s size, check the index calculations, and ensure proper bounds checking before accessing array elements.