Can't add new servers to existing cluster

[PeterJM]

We have a 12 node cluster running 6.5 SP8 with SecurePath installed on QLogic HBAs. We have just built 4 new servers with the same OS versions except we want to use MPIO. However when we try to add the servers into the existing cluster it prompts the message "Cluster Services Partition has been detected that is not visible on the following servers". Doing a "List Devices" on one of the new servers shows the same LUNs as presented to the other servers except it shows two "Unbound Device Objects"?
Is it possible to run MPIO on some servers and Securepath on others?
Or is their some other reason why I can't add the new servers?

Any ideas much appreciated.

Thanks.