According to the below document, you should use Oracle Forms & Reports 11g.
It is supported with all R12 releases (12.0, 12.1, and 12.2)
Is Oracle Developer Suite 11g (Forms and Reports) Supported for Oracle E-Business Suite 12i? (Doc ID 1610344.1)
Unfortunately the MOS Doc is incorrect - currently only 10.1.2.x is supported with EBS R12.x
Will have this rectified.