Thanks guys... I did get it in the end... To start with I had the poison made but it wouldn't count towards the writ... That's why I posted and asked for the help... I thought they had to be in order... But when I tried again today it seemed to allow it...
Thanks for the help tho

Alkahest, Lady's Smock, Namira's Rot, Violet Caprinus

Use Violet Coprinus, Lady's Smock and either Namira's Rot OR Water Hyacint, plus alkahest. The order of ingredients does not matter.

The logic behind alchemy potions is to bring in the effect at least twice without counter-effect (like magicka vs. ravage magicka). Look at the tooltips of ingredients and select one if it has at least two of the effects.

This particular potion comes up from following ingredients
- Lady's Smock is first because it has all threee effects. This is a little different from normal 2+2+2 effects. That relaxes the requirement for last ingredient, but the second ingredient need still bring in two effects.
- Violet Coprinus is only possible choice for second ingredient because no other brings in two effects. It gives Breach and Spell Power and now the two efects are fulfilled. Only Spell Crit is still missing.
- Either Namira's Rot or Water Hyacint bring in Spell Critical
- Use Alkahest to make a poison

Now each effect is in twice in ingredients. Beetle Scuttle does have Breach but nothing else. That's why it's unsuitable.

As a last check, put the ingredients into table and double-check that the name of the potion/poison really matches the quest.