1) PowerPath 3.0 is quote old now and you may need to run a "powercf -q" followed by "powermt config" to correctly integrate new devices.
2) Do you have a Celerra on your site? Has this "new" disk been previously used by the Celerra? If so, the Celerra signature may still be present on the disk and PowerPath will "hide" it from the host OS. To check whether this is the case, run "powerprotect format" and see if its visible then. If it is - you may need to have the volume VTOC'd (formatted) from the Symm to clear the Celerra signature which is at the end of the volume.
Good to hear its sorted. It was almost certainly the Celerra label issue. If you have this again, refer the support lab to Knowledgebase article emc90082 for details on how to remove the Celerra signature.
Another option is to have your CE VTOC the affected volumes.