The problem is that you're code is trying to copy the old OID to the new record (which can't be done as this is a non-editable field and it's value is automatically generated by Arc). You need to put in a check to see if the field is editable, if it's not then don't assign a value to it, you can use IField.Editable for this.
Also, I noticed a couple of problems with your code, you're creating an empty polyline to store in the featureclass, although this may work, you wont be able to see anything in your map! The other thing is that you're assigning this geometry inside the fields loop, it only needs to be done once, outside the loop.
hope that helps,