BCS Comments on Entenring Manual Documents

Hi experts,

When I execute a Manual Posting under UCMON, the tab "Comment" doesn't give me any option to include the comments. It is totally gray.

In SAP help I found out it's supposed to configure InfoObject 0AC_DOCNR with "Characteristic is Doc. Attribute indicator" in the General tab (in RSA1).

Even with that I still don't have the option of including any comments. Am I missing something?

Thanks in advance for any help.