AP-Credit Memo-Clear Vendor/Credit Memo

Hi all, I am facing Problem during Vendor Credit memo, Clear it (F-44), and Manual Check using F-58

Can I have different Due date For Vendor Credit memo , as I can see we have different Payment terms in Master data but whenever I post it gives the Due date as Immediate but if I see Open item report it says not Due and shows the Payment terms and the net due dates. Is this Normal?

I would like to clear the credit memo using the F-44 with reference to another open line item but system says Difference is too large for clearing.

The third thing I am trying to issue manual check I gave details, as per "J03_AP_CreditMemo_BPP_EN_US", when I hit Process open Items "system is not allowing to post document getting error "Select a valid function"".

Any Ideas How to deal with the above 3 situations?

Sandhya.