sales document xxxx currently being edited by xxxx

I get the error sales document xxxx currently being edited by xxxx in bapi_sales_order_change though the sales order being processed are not opened simultaneously. Based on previous suggestions and other techniques,

The following have been already taken care of:

1. Explicitly handling and releasing the lock for the given sales order with all other parameters as default.

I am locking it before bapi_billing_cancel1 and releasing it after bapi commit. Enqueue before sales order and dequeue after committing bapi_sales_order_change.

2. Refreshing the data.

3. Explicit wait time as buffer ( wait up to 5 seconds ) on top of BAPI wait time

Do you have any other suggestions to work around a way with out actually increasing the buffer time.

Any input will be helpful.