BAPI_SALESORDER_SIMULATE is hangs up when running for multiple users

Hi SAP Gurus,

I am using BAPI_SALESORDER_SIMULATE for price repricing . However when multiple users or same user runs in multiple sessions, one session will run , however other sessions till it reaches BAPI it is fast and once it enters to BAPI, it got hangs up or keeps running & not giving any output.

Any thoughts how i can impove the performace for muliple users when i am using this BAPI.

Here are the details i am sending to BAPI .

call function 'BAPI_SALESORDER_SIMULATE'

exporting

order_header_in = lv_sd_order_header

importing

return = lv_return

tables

order_items_in = lit_sd_order_items_in

order_partners = lit_sd_order_partners

order_schedule_in = lit_sd_order_schdl_in

order_items_out = lit_sd_order_items_out

order_condition_ex = lit_sd_order_condition.

Your thoughts most appricated.

Regards

Harikrishna