In standard behaviour, if a dimension is set as code mandatory for G/L accounts and doesn't have a Dimension Value Code set (is empty, so the dimension is set as mandatory, but it can be any value defined per document) it's not possible to run and post the VAT settlement, because the dimension is set as mandatory, However, there's no field to fill and set the dimension.

So, it should exist a boolean field "Ignore dimensions" to set as true when calculating and post VAT settlement, so it's possible to do it without error.