Hi Dawood,
I have tested with same your case.
I put mandatory for Reference and Header text for document type SA, and I can post KB11N without error.
Can you check any validation effect to this case? (tcode OB28)
One more thing:
The repost in KB11N only created Controlling document, it's not effect to FI document.
Example:
In FI document:
Expense - CCtr 1
You repost in KB11N
Expense - CCtr 1 to CCtr 2.
When you display FI document, the CO object always be CCtr1.
If you cannot reverse document, please post FI document through F-02 with:
Debit Expense - CCtr 2
Credit Expense - CCtr 1.
Julie