Hi
1) I guess BBP_BW_GET_APPR_LIMIT returns the approval limit settings from the transaction SU01 -'Personalization' and BBP_APPROVAL_LIMIT variable. Did you try to set that for the users where it did not fetch it (set in SU01).
2) Also check if this FM has been released for customer use or not or whether it is meant for SAP coding only. Check table TFDIR-FREEDATE if value is there, it means release else not. (I do not have a SRM system currently to check that).
You can refer note 109533 - Use of SAP function modules for things to keep in mind when using non-released FMs.
3) If the Approval Limit is set in the Org Structure, you can try using FM BBP_READ_ATTRIBUTES.
4) Also, whenever you post such upgrade questions, it is always good to mention what release you were on and what is the current release.
regards,
Modak