Cannot delete or add payment categories

Hi,

I have two issues with payment categories:

1. There are duplicate categories for "solo money account". They are identical, so I want to delete duplicates, but when I try I get the following error: "Unable to delete this category. This category has transactions or it's needed for your accounting purposes". I assume this is because there are some expenses codes to the category. Is there any way to work around this?
2. I have added a payment category for my superannuation fund. It appears in my "all categories" list in settings, but does not appear as an option when trying to record an invoice payment. What am I not doing here?

Thanks

Sean.