Is the Endpoint Protection Small Business Edition 12.0 now no longer support the block USB Storage Devices using an Application Policy?
SEP SMB 12.0 Never had supported USB blocking
There is no option to control USB ports and other peripherals in Symantec Endpoint Protection 12.0, since there no Application and Device control policy is available in that version.
https://www-secure.symantec.com/connect/articles/symantec-endpoint-protection-small-business-edition-120-frequently-asked-questions