Usually error 100, indicates what it means. This is, maybe u are trying to link a credit note to a invoice that already has been linked to the same credit note.
By the other hand, maybe this is caused by a bug on the session. U should veryfy the what of the session and contact with ssa global support to obtain the latest object for this particular session.
Also u can check on the $BSE/log directory to see a more detailed explanation.
At first sight, u are obtaining the error on tfacp200, In this table the system registers all the invoices and also all the payments, credit notes etc.
Hope this help.
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