Estimate Errors?

I think I am hitting two distinct errors while trying to produce estimates:

FIRST
1. If I set up an inventory discount item choosing VAT (Sales TAx) Code VAT:S
2. Create an estimate using standard forms.
3. Choose my discount item and set it to any -%.
4. Save and Print
Result: Error message - "you have hit an unexpected error etc".  The same does not happen if I use the Partner Discount in the same way.

SECOND
1. Create an estimate using standard forms.
2. Use Partner Discount at any -%age.
3. Save and Print
Result: I get the pre-VAT (Sales Tax) figure calculated as per discount, but the VAT payable ignores the discount calculation (i.e. is calculated on the gross figure).