Like Byz said, 78 refers to your freeplayer bank space, which you've filled, and that's why you can't put anything more into your bank.
When someone has more than 78 freeplay items, they start to count towards the item count in the member's-only bank space. If that's the case here and you have more than 78 freeplay items, then you'll need to drop enough items to get yourself under the freeplay limit again.
But it doesn't look like you'll need to drop as many as 25. I see you still have some member's items; it used to be the case that member's items could cause a freeplayer's bank to be over the limit, but nowadays as long as you have less than the allotted 468 member's items, then they won't have any impact on your bank while you're a freeplayer.
In other words: keep your member's stuff, drop some freeplay stuff.