10001155 
Message
Serial number [serial number] already in use; select new serial number
Diagnosis
You have attempted to create a purchasing document for a serial number managed item, but the serial number you tried to use has already been assigned to this item in the same purchasing document. You cannot create a serial number that is already in use in the inventory.
For example, you have followed the steps below:
You have created a delivery document for an item managed by serial numbers, and you have assigned a serial number to the item. You then added the delivery document.
You have created a return document, and you have assigned the same serial number to the same item as in step 1. You have not added the return document.
You have created another return document. You have assigned the same serial number to the same item as in step 1 and step 2 and you have added the document. Since you have not added the return document in step 2, the return document has the same document number as the return document you created in step 2.
You have tried to add the return document you have created in step 2, but you have received this error message.
Procedure
Follow the steps below:
In the purchasing document, in the item row, press CTRL+TAB in the Quantity field. The Define Serial Numbers window appears.
Specify a new serial number and choose the OK button to update the item in the purchasing document.