The serial number of the AP is missing in the show version command output after upgrade from VxWorks to Cisco IOS .
When upgrading a 350 or 1200 Access Point (AP) running VxWorks to Cisco IOS using the conversion tool, some of the fields are not updated. During the AP's power-up sequence after an upgrade to Cisco IOS Software, some fields reported in the console messages are blank or are populated with zeros. Blank or zero fields are normal after a successful upgrade because 350 and 1200 series APs do not support that information. Some of the fields which are not updated after the upgrade to Cisco IOS include Part Number, PCB Serial Number, Top Assembly Serial Number, among others.
Note: You cannot get the serial number of the device back after the upgrade. You cannot view the serial number of the device by issuing the show version command. This upgrade is permanent. You cannot downgrade to VxWorks from Cisco IOS Software since the VxWorks bootloader is overwritten during the upgrade process.