C++ pointer not null but cannot be freed

I'm implementing an open HashTable. My trouble arises in the destructor, where I iterate through all the buckets in an array, for each array I would delete all the nodes in a linked list.

        // Deallocate all buckets
        for (int i=0; i<maxBuckets; i++) {
            Cell * p = m_data[i];
            while (p != nullptr) {

                Cell * temp = p;
                p = p->next;
                delete temp;
            }
        }
        delete [] m_data;

But it reports pointer being freed was not allocated on the delete operation. What is going wrong here?

The error is pretty clear. You tried to delete a value that was not returned by new.

What we don't know is if the value is the address of a non-allocated value, just uninitialized (garbage) or if you've corrupted the heap. You haven't provided information to determine that.

But you do know that the value you are trying to free is not correct, and you need to figure out where it came from.