Saba,
I have the same situation when using a newer ABAP Stack with SAP PI 7.4 AEX. When you have the option to maintain a HTTP Destination in SLDAPICUST this and specifying SAP_PROXY_ESR should suffice on configuration. But when you delete SAPSLDAPI / LCRSAPRFC I'm getting the error you mentioned.
Did you find a solution to this / did you resolve this?
Many thanks
Cheers
Jens