Issue with userdefined field in Orders.Line object

Hi, your piece of SW works fine and could create Orders in SAP b1 thanks a lot, however whenever tried insert a Order Line userfield item as follow got an error, even whe this syntax works fine at the Order level Order Level (Header) -> order.UserFields.Fields.Item("U_CMP_MATR").Value = "TEST" -> Works fine
but not in the Order Lines Detail -> order.Lines.UserFields.Fields.Item("U_CMP_MATR").Value = "TEST" -> error...and crash the application.

Please can you let us know what are we doing wrong ? Thanks in advance.

Sorry to reply late. The issue should be related to the memory of the system. What is the configuration of your server?